From 8b1d6eb7cfff798b0fd055b58be2eb97ede5932f Mon Sep 17 00:00:00 2001
From: Thatsaphorn Atchariyaphap <thatsaphorn@outlook.de>
Date: Sun, 27 Apr 2025 17:42:02 +0000
Subject: [PATCH] Backend migration

---
 .run/ContactServiceApplication.run.xml        |  18 +++
 .run/DiscoveryServerApplication.run.xml       |  15 ++
 .run/Gateway.run.xml                          |   7 +
 .run/GatewayApplication.run.xml               |  18 +++
 .run/MailServiceApplication.run.xml           |  15 ++
 .run/npm-dev.run.xml                          |  12 ++
 backend/.gitignore                            |  40 +++++
 backend/discoveryServer/pom.xml               |  32 ++++
 .../DiscoveryServerApplication.java           |  19 +++
 .../src/main/resources/application.yml        |  13 ++
 backend/gateway/pom.xml                       |  82 ++++++++++
 .../rheinsw/gateway/GatewayApplication.java   |  15 ++
 .../gateway/filter/ApiKeyGatewayFilter.java   |  85 ++++++++++
 .../dev/rheinsw/gateway/model/ApiKey.java     |  61 ++++++++
 .../dev/rheinsw/gateway/model/ApiKeyType.java |  10 ++
 .../gateway/repository/ApiKeyRepository.java  |  14 ++
 .../gateway/service/ApiKeyValidator.java      |  27 ++++
 .../src/main/resources/application.yml        |  41 +++++
 .../db/migration/V1__add-api-key-schema.sql   |  58 +++++++
 .../filter/ApiKeyGatewayFilterTest.java       | 121 ++++++++++++++
 .../gateway/security/ApiKeyValidatorTest.java |  51 ++++++
 .../src/test/resources/application.yml        |   1 +
 backend/placeholder                           |   0
 backend/pom.xml                               |  83 ++++++++++
 backend/services/contactService/pom.xml       | 100 ++++++++++++
 .../ContactServiceApplication.java            |  19 +++
 .../contactService/config/HCaptchaConfig.java |  19 +++
 .../controller/ContactController.java         | 114 ++++++++++++++
 .../contactService/dto/ContactRequestDto.java |  18 +++
 .../contactService/model/ContactRequest.java  |  95 +++++++++++
 .../repository/ContactRequestsRepo.java       |  12 ++
 .../service/HCaptchaValidator.java            |  55 +++++++
 .../src/main/resources/application.yml        |  31 ++++
 .../db/migration/V1__create_tables.sql        |  12 ++
 .../controller/ContactControllerTest.java     | 125 +++++++++++++++
 .../service/HCaptchaValidatorTest.java        | 147 ++++++++++++++++++
 backend/services/mailService/pom.xml          | 114 ++++++++++++++
 .../rheinsw/mail/MailServiceApplication.java  |  18 +++
 .../mail/controller/MailController.java       |  33 ++++
 .../dev/rheinsw/mail/service/MailService.java |  33 ++++
 .../src/main/resources/application.yml        |  24 +++
 .../mail/controller/MailControllerTest.java   |  63 ++++++++
 .../rheinsw/mail/service/MailServiceTest.java |  60 +++++++
 backend/shared/pom.xml                        |  88 +++++++++++
 .../dev/rheinsw/shared/entity/BaseEntity.java |  37 +++++
 .../shared/mail/MailServiceClient.java        |  50 ++++++
 .../rheinsw/shared/mail/dto/MailRequest.java  |  20 +++
 .../shared/rest/RestTemplateConfig.java       |  20 +++
 .../dev/rheinsw/shared/transport/Dto.java     |  10 ++
 .../rheinsw/shared/entity/BaseEntityTest.java |  58 +++++++
 .../shared/mail/MailServiceClientTest.java    |  83 ++++++++++
 .../shared/rest/RestTemplateConfigTest.java   |  30 ++++
 52 files changed, 2326 insertions(+)
 create mode 100644 .run/ContactServiceApplication.run.xml
 create mode 100644 .run/DiscoveryServerApplication.run.xml
 create mode 100644 .run/Gateway.run.xml
 create mode 100644 .run/GatewayApplication.run.xml
 create mode 100644 .run/MailServiceApplication.run.xml
 create mode 100644 .run/npm-dev.run.xml
 create mode 100644 backend/.gitignore
 create mode 100644 backend/discoveryServer/pom.xml
 create mode 100644 backend/discoveryServer/src/main/java/dev/rheinsw/discoveryServer/DiscoveryServerApplication.java
 create mode 100644 backend/discoveryServer/src/main/resources/application.yml
 create mode 100644 backend/gateway/pom.xml
 create mode 100644 backend/gateway/src/main/java/dev/rheinsw/gateway/GatewayApplication.java
 create mode 100644 backend/gateway/src/main/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilter.java
 create mode 100644 backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKey.java
 create mode 100644 backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKeyType.java
 create mode 100644 backend/gateway/src/main/java/dev/rheinsw/gateway/repository/ApiKeyRepository.java
 create mode 100644 backend/gateway/src/main/java/dev/rheinsw/gateway/service/ApiKeyValidator.java
 create mode 100644 backend/gateway/src/main/resources/application.yml
 create mode 100644 backend/gateway/src/main/resources/db/migration/V1__add-api-key-schema.sql
 create mode 100644 backend/gateway/src/test/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilterTest.java
 create mode 100644 backend/gateway/src/test/java/dev/rheinsw/gateway/security/ApiKeyValidatorTest.java
 create mode 100644 backend/gateway/src/test/resources/application.yml
 delete mode 100644 backend/placeholder
 create mode 100644 backend/pom.xml
 create mode 100644 backend/services/contactService/pom.xml
 create mode 100644 backend/services/contactService/src/main/java/dev/rheinsw/contactService/ContactServiceApplication.java
 create mode 100644 backend/services/contactService/src/main/java/dev/rheinsw/contactService/config/HCaptchaConfig.java
 create mode 100644 backend/services/contactService/src/main/java/dev/rheinsw/contactService/controller/ContactController.java
 create mode 100644 backend/services/contactService/src/main/java/dev/rheinsw/contactService/dto/ContactRequestDto.java
 create mode 100644 backend/services/contactService/src/main/java/dev/rheinsw/contactService/model/ContactRequest.java
 create mode 100644 backend/services/contactService/src/main/java/dev/rheinsw/contactService/repository/ContactRequestsRepo.java
 create mode 100644 backend/services/contactService/src/main/java/dev/rheinsw/contactService/service/HCaptchaValidator.java
 create mode 100644 backend/services/contactService/src/main/resources/application.yml
 create mode 100644 backend/services/contactService/src/main/resources/db/migration/V1__create_tables.sql
 create mode 100644 backend/services/contactService/src/test/java/dev/rheinsw/contactService/controller/ContactControllerTest.java
 create mode 100644 backend/services/contactService/src/test/java/dev/rheinsw/contactService/service/HCaptchaValidatorTest.java
 create mode 100644 backend/services/mailService/pom.xml
 create mode 100644 backend/services/mailService/src/main/java/dev/rheinsw/mail/MailServiceApplication.java
 create mode 100644 backend/services/mailService/src/main/java/dev/rheinsw/mail/controller/MailController.java
 create mode 100644 backend/services/mailService/src/main/java/dev/rheinsw/mail/service/MailService.java
 create mode 100644 backend/services/mailService/src/main/resources/application.yml
 create mode 100644 backend/services/mailService/src/test/java/dev/rheinsw/mail/controller/MailControllerTest.java
 create mode 100644 backend/services/mailService/src/test/java/dev/rheinsw/mail/service/MailServiceTest.java
 create mode 100644 backend/shared/pom.xml
 create mode 100644 backend/shared/src/main/java/dev/rheinsw/shared/entity/BaseEntity.java
 create mode 100644 backend/shared/src/main/java/dev/rheinsw/shared/mail/MailServiceClient.java
 create mode 100644 backend/shared/src/main/java/dev/rheinsw/shared/mail/dto/MailRequest.java
 create mode 100644 backend/shared/src/main/java/dev/rheinsw/shared/rest/RestTemplateConfig.java
 create mode 100644 backend/shared/src/main/java/dev/rheinsw/shared/transport/Dto.java
 create mode 100644 backend/shared/src/test/java/dev/rheinsw/shared/entity/BaseEntityTest.java
 create mode 100644 backend/shared/src/test/java/dev/rheinsw/shared/mail/MailServiceClientTest.java
 create mode 100644 backend/shared/src/test/java/dev/rheinsw/shared/rest/RestTemplateConfigTest.java

diff --git a/.run/ContactServiceApplication.run.xml b/.run/ContactServiceApplication.run.xml
new file mode 100644
index 0000000..52ea1bd
--- /dev/null
+++ b/.run/ContactServiceApplication.run.xml
@@ -0,0 +1,18 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="ContactServiceApplication" type="SpringBootApplicationConfigurationType" factoryName="Spring Boot" nameIsGenerated="true">
+    <envs>
+      <env name="INTERNAL_API_KEY" value="LXuEOniIKfCktZObOkxRbJOL8O9xUwKLtW1stDXDBMj0nbpNPkPlC4Tnj3C9RSNg" />
+    </envs>
+    <module name="contactService" />
+    <option name="SPRING_BOOT_MAIN_CLASS" value="dev.rheinsw.contactService.ContactServiceApplication" />
+    <extension name="coverage">
+      <pattern>
+        <option name="PATTERN" value="dev.rheinsw.contactService.*" />
+        <option name="ENABLED" value="true" />
+      </pattern>
+    </extension>
+    <method v="2">
+      <option name="Make" enabled="true" />
+    </method>
+  </configuration>
+</component>
\ No newline at end of file
diff --git a/.run/DiscoveryServerApplication.run.xml b/.run/DiscoveryServerApplication.run.xml
new file mode 100644
index 0000000..2b19ee2
--- /dev/null
+++ b/.run/DiscoveryServerApplication.run.xml
@@ -0,0 +1,15 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="DiscoveryServerApplication" type="SpringBootApplicationConfigurationType" factoryName="Spring Boot" nameIsGenerated="true">
+    <module name="discoveryServer" />
+    <option name="SPRING_BOOT_MAIN_CLASS" value="dev.rheinsw.discoveryServer.DiscoveryServerApplication" />
+    <extension name="coverage">
+      <pattern>
+        <option name="PATTERN" value="dev.rheinsw.discoveryServer.*" />
+        <option name="ENABLED" value="true" />
+      </pattern>
+    </extension>
+    <method v="2">
+      <option name="Make" enabled="true" />
+    </method>
+  </configuration>
+</component>
\ No newline at end of file
diff --git a/.run/Gateway.run.xml b/.run/Gateway.run.xml
new file mode 100644
index 0000000..0a00370
--- /dev/null
+++ b/.run/Gateway.run.xml
@@ -0,0 +1,7 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Gateway" type="CompoundRunConfigurationType">
+    <toRun name="DiscoveryServerApplication" type="SpringBootApplicationConfigurationType" />
+    <toRun name="GatewayApplication" type="SpringBootApplicationConfigurationType" />
+    <method v="2" />
+  </configuration>
+</component>
\ No newline at end of file
diff --git a/.run/GatewayApplication.run.xml b/.run/GatewayApplication.run.xml
new file mode 100644
index 0000000..75480c1
--- /dev/null
+++ b/.run/GatewayApplication.run.xml
@@ -0,0 +1,18 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="GatewayApplication" type="SpringBootApplicationConfigurationType" factoryName="Spring Boot" nameIsGenerated="true">
+    <envs>
+      <env name="FRONTEND_ORIGIN" value="http://localhost:3000 " />
+    </envs>
+    <module name="gateway" />
+    <option name="SPRING_BOOT_MAIN_CLASS" value="dev.rheinsw.gateway.GatewayApplication" />
+    <extension name="coverage">
+      <pattern>
+        <option name="PATTERN" value="dev.rheinsw.gateway.*" />
+        <option name="ENABLED" value="true" />
+      </pattern>
+    </extension>
+    <method v="2">
+      <option name="Make" enabled="true" />
+    </method>
+  </configuration>
+</component>
\ No newline at end of file
diff --git a/.run/MailServiceApplication.run.xml b/.run/MailServiceApplication.run.xml
new file mode 100644
index 0000000..868a7ba
--- /dev/null
+++ b/.run/MailServiceApplication.run.xml
@@ -0,0 +1,15 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="MailServiceApplication" type="SpringBootApplicationConfigurationType" factoryName="Spring Boot" nameIsGenerated="true">
+    <module name="mailService" />
+    <option name="SPRING_BOOT_MAIN_CLASS" value="dev.rheinsw.mail.MailServiceApplication" />
+    <extension name="coverage">
+      <pattern>
+        <option name="PATTERN" value="dev.rheinsw.mail.*" />
+        <option name="ENABLED" value="true" />
+      </pattern>
+    </extension>
+    <method v="2">
+      <option name="Make" enabled="true" />
+    </method>
+  </configuration>
+</component>
\ No newline at end of file
diff --git a/.run/npm-dev.run.xml b/.run/npm-dev.run.xml
new file mode 100644
index 0000000..7e6ed4c
--- /dev/null
+++ b/.run/npm-dev.run.xml
@@ -0,0 +1,12 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="npm-dev" type="js.build_tools.npm">
+    <package-json value="$PROJECT_DIR$/frontend/package.json" />
+    <command value="run" />
+    <scripts>
+      <script value="dev" />
+    </scripts>
+    <node-interpreter value="project" />
+    <envs />
+    <method v="2" />
+  </configuration>
+</component>
\ No newline at end of file
diff --git a/backend/.gitignore b/backend/.gitignore
new file mode 100644
index 0000000..eef3e3a
--- /dev/null
+++ b/backend/.gitignore
@@ -0,0 +1,40 @@
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
+/.idea/
+/.env
diff --git a/backend/discoveryServer/pom.xml b/backend/discoveryServer/pom.xml
new file mode 100644
index 0000000..f18e5e1
--- /dev/null
+++ b/backend/discoveryServer/pom.xml
@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>dev.rheinsw</groupId>
+        <artifactId>rheinsw-backend</artifactId>
+        <version>1.0.0</version>
+    </parent>
+
+    <artifactId>discoveryServer</artifactId>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.cloud</groupId>
+            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter</artifactId>
+        </dependency>
+    </dependencies>
+
+</project>
\ No newline at end of file
diff --git a/backend/discoveryServer/src/main/java/dev/rheinsw/discoveryServer/DiscoveryServerApplication.java b/backend/discoveryServer/src/main/java/dev/rheinsw/discoveryServer/DiscoveryServerApplication.java
new file mode 100644
index 0000000..c829966
--- /dev/null
+++ b/backend/discoveryServer/src/main/java/dev/rheinsw/discoveryServer/DiscoveryServerApplication.java
@@ -0,0 +1,19 @@
+package dev.rheinsw.discoveryServer;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;
+
+/**
+ * @author Bummsa / BoomerHD / Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+@SpringBootApplication
+@EnableEurekaServer
+public class DiscoveryServerApplication {
+
+    public static void main(String[] args) {
+        SpringApplication.run(DiscoveryServerApplication.class, args);
+    }
+
+}
\ No newline at end of file
diff --git a/backend/discoveryServer/src/main/resources/application.yml b/backend/discoveryServer/src/main/resources/application.yml
new file mode 100644
index 0000000..0951837
--- /dev/null
+++ b/backend/discoveryServer/src/main/resources/application.yml
@@ -0,0 +1,13 @@
+server:
+  port: 8761
+
+spring:
+  application:
+    name: discovery-server
+
+eureka:
+  client:
+    register-with-eureka: false
+    fetch-registry: false
+  server:
+    wait-time-in-ms-when-sync-empty: 0
diff --git a/backend/gateway/pom.xml b/backend/gateway/pom.xml
new file mode 100644
index 0000000..0087160
--- /dev/null
+++ b/backend/gateway/pom.xml
@@ -0,0 +1,82 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>dev.rheinsw</groupId>
+        <artifactId>rheinsw-backend</artifactId>
+        <version>1.0.0</version>
+    </parent>
+
+    <artifactId>gateway</artifactId>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.springframework.cloud</groupId>
+            <artifactId>spring-cloud-starter-gateway</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.cloud</groupId>
+            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-data-jpa</artifactId>
+        </dependency>
+
+        <!-- Other Tools -->
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.postgresql</groupId>
+            <artifactId>postgresql</artifactId>
+        </dependency>
+
+        <!-- Tests -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.h2database</groupId>
+            <artifactId>h2</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.wiremock</groupId>
+            <artifactId>wiremock-standalone</artifactId>
+            <version>3.13.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>dev.rheinsw</groupId>
+            <artifactId>shared</artifactId>
+            <version>1.0.0</version>
+            <scope>compile</scope>
+        </dependency>
+
+    </dependencies>
+</project>
\ No newline at end of file
diff --git a/backend/gateway/src/main/java/dev/rheinsw/gateway/GatewayApplication.java b/backend/gateway/src/main/java/dev/rheinsw/gateway/GatewayApplication.java
new file mode 100644
index 0000000..7a1dd61
--- /dev/null
+++ b/backend/gateway/src/main/java/dev/rheinsw/gateway/GatewayApplication.java
@@ -0,0 +1,15 @@
+package dev.rheinsw.gateway;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * @author Bummsa / BoomerHD / Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+@SpringBootApplication
+public class GatewayApplication {
+    public static void main(String[] args) {
+        SpringApplication.run(GatewayApplication.class, args);
+    }
+}
\ No newline at end of file
diff --git a/backend/gateway/src/main/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilter.java b/backend/gateway/src/main/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilter.java
new file mode 100644
index 0000000..8672a81
--- /dev/null
+++ b/backend/gateway/src/main/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilter.java
@@ -0,0 +1,85 @@
+package dev.rheinsw.gateway.filter;
+
+import dev.rheinsw.gateway.service.ApiKeyValidator;
+import lombok.RequiredArgsConstructor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.cloud.gateway.filter.GlobalFilter;
+import org.springframework.cloud.gateway.route.Route;
+import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
+import org.springframework.core.annotation.Order;
+import org.springframework.http.HttpStatus;
+import org.springframework.stereotype.Component;
+import org.springframework.web.server.ServerWebExchange;
+import reactor.core.publisher.Mono;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 24.04.25
+ */
+@Component
+@Order(-1)
+@RequiredArgsConstructor
+public class ApiKeyGatewayFilter implements GlobalFilter {
+
+    private static final Logger log = LoggerFactory.getLogger(ApiKeyGatewayFilter.class);
+
+    @Value("${gateway.security.frontend-origin}")
+    private String expectedFrontendOrigin;
+
+    private final ApiKeyValidator apiKeyValidator;
+
+    @Override
+    public Mono<Void> filter(ServerWebExchange exchange, org.springframework.cloud.gateway.filter.GatewayFilterChain chain) {
+        String path = exchange.getRequest().getURI().getPath();
+        log.debug("Incoming request for path: {}", path);
+
+        if (path.startsWith("/api/public/")) {
+            log.debug("Public path detected, skipping API key validation");
+            return chain.filter(exchange);
+        }
+
+        String frontendKey = exchange.getRequest().getHeaders().getFirst("X-Frontend-Key");
+        String internalKey = exchange.getRequest().getHeaders().getFirst("X-Internal-Auth");
+        String targetService = resolveTargetServiceFromExchange(exchange);
+        boolean isFrontend = isFrontendRequest(exchange);
+
+        log.debug("Target service resolved: {}, isFrontend: {}", targetService, isFrontend);
+
+        if (frontendKey != null && isFrontend) {
+            log.debug("Validating frontend API key for service: {}", targetService);
+            if (apiKeyValidator.isAuthorized(frontendKey, targetService, true)) {
+                log.debug("Frontend API key authorized");
+                return chain.filter(exchange);
+            }
+            log.warn("Shared API key validation failed for service: {}", targetService);
+        }
+
+        if (internalKey != null) {
+            log.debug("Validating internal API key for service: {}", targetService);
+            if (apiKeyValidator.isAuthorized(internalKey, targetService, false)) {
+                log.debug("Internal API key authorized");
+                return chain.filter(exchange);
+            }
+            log.warn("Internal API key validation failed for service: {}", targetService);
+        }
+
+        log.warn("Unauthorized request to {} from origin {}", path, exchange.getRequest().getHeaders().getFirst("Origin"));
+        exchange.getResponse().setStatusCode(HttpStatus.UNAUTHORIZED);
+        return exchange.getResponse().setComplete();
+    }
+
+    private String resolveTargetServiceFromExchange(ServerWebExchange exchange) {
+        Route route = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR);
+        return route != null ? route.getId() : "unknown";
+    }
+
+    private boolean isFrontendRequest(ServerWebExchange exchange) {
+        String origin = exchange.getRequest().getHeaders().getFirst("Origin");
+        boolean matches = origin != null && origin.trim().equalsIgnoreCase(expectedFrontendOrigin.trim());
+        log.debug("Origin header: {}, expected: {}, matches: {}", origin, expectedFrontendOrigin, matches);
+        return matches;
+    }
+
+}
diff --git a/backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKey.java b/backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKey.java
new file mode 100644
index 0000000..38437de
--- /dev/null
+++ b/backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKey.java
@@ -0,0 +1,61 @@
+package dev.rheinsw.gateway.model;
+
+import dev.rheinsw.shared.entity.BaseEntity;
+import jakarta.persistence.CollectionTable;
+import jakarta.persistence.Column;
+import jakarta.persistence.ElementCollection;
+import jakarta.persistence.Entity;
+import jakarta.persistence.EnumType;
+import jakarta.persistence.Enumerated;
+import jakarta.persistence.FetchType;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.JoinColumn;
+import jakarta.persistence.Table;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
+import java.util.Set;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 25.04.25
+ */
+@Entity
+@Table(name = "api_key")
+@Getter
+@Setter
+@NoArgsConstructor
+@AllArgsConstructor
+@Builder
+public class ApiKey extends BaseEntity {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(name = "api_key", unique = true, nullable = false)
+    private String apiKey;
+
+    @Enumerated(EnumType.STRING)
+    @Column(nullable = false)
+    private ApiKeyType type;
+
+    @ElementCollection(fetch = FetchType.EAGER)
+    @CollectionTable(name = "api_key_services", joinColumns = @JoinColumn(name = "api_key_id"))
+    @Column(name = "allowed_service")
+    private Set<String> allowedServices;
+
+    @Column(nullable = false)
+    private boolean enabled;
+
+    @Column(name = "frontend_only", nullable = false)
+    private boolean frontendOnly;
+
+    @Column
+    private String description;
+}
diff --git a/backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKeyType.java b/backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKeyType.java
new file mode 100644
index 0000000..3e8d411
--- /dev/null
+++ b/backend/gateway/src/main/java/dev/rheinsw/gateway/model/ApiKeyType.java
@@ -0,0 +1,10 @@
+package dev.rheinsw.gateway.model;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 25.04.25
+ */
+public enum ApiKeyType {
+    FRONTEND,
+    INTERNAL;
+}
diff --git a/backend/gateway/src/main/java/dev/rheinsw/gateway/repository/ApiKeyRepository.java b/backend/gateway/src/main/java/dev/rheinsw/gateway/repository/ApiKeyRepository.java
new file mode 100644
index 0000000..4ec2fda
--- /dev/null
+++ b/backend/gateway/src/main/java/dev/rheinsw/gateway/repository/ApiKeyRepository.java
@@ -0,0 +1,14 @@
+package dev.rheinsw.gateway.repository;
+
+import dev.rheinsw.gateway.model.ApiKey;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.Optional;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 25.04.25
+ */
+public interface ApiKeyRepository extends JpaRepository<ApiKey, Long> {
+    Optional<ApiKey> findByApiKey(String apiKey);
+}
\ No newline at end of file
diff --git a/backend/gateway/src/main/java/dev/rheinsw/gateway/service/ApiKeyValidator.java b/backend/gateway/src/main/java/dev/rheinsw/gateway/service/ApiKeyValidator.java
new file mode 100644
index 0000000..96dd478
--- /dev/null
+++ b/backend/gateway/src/main/java/dev/rheinsw/gateway/service/ApiKeyValidator.java
@@ -0,0 +1,27 @@
+package dev.rheinsw.gateway.service;
+
+import dev.rheinsw.gateway.model.ApiKey;
+import dev.rheinsw.gateway.repository.ApiKeyRepository;
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import org.springframework.stereotype.Service;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 25.04.25
+ */
+@Service
+@RequiredArgsConstructor
+@Slf4j
+public class ApiKeyValidator {
+
+    private final ApiKeyRepository apiKeyRepository;
+
+    public boolean isAuthorized(String key, String targetService, boolean isFrontendRequest) {
+        return apiKeyRepository.findByApiKey(key)
+                .filter(ApiKey::isEnabled)
+                .filter(apiKey -> !apiKey.isFrontendOnly() || isFrontendRequest)
+                .filter(apiKey -> apiKey.getAllowedServices().contains(targetService))
+                .isPresent();
+    }
+}
diff --git a/backend/gateway/src/main/resources/application.yml b/backend/gateway/src/main/resources/application.yml
new file mode 100644
index 0000000..e9371f2
--- /dev/null
+++ b/backend/gateway/src/main/resources/application.yml
@@ -0,0 +1,41 @@
+server:
+  port: 8080
+
+eureka:
+  client:
+    service-url:
+      defaultZone: http://localhost:8761/eureka/
+
+gateway:
+  security:
+    frontend-origin: ${FRONTEND_ORIGIN}
+
+spring:
+  application:
+    name: gateway
+  datasource:
+    url: jdbc:postgresql://localhost:5432/rheinsw_dev
+    username: rheinsw
+    password: rheinsw
+  jpa:
+    hibernate:
+      ddl-auto: none
+    show-sql: true
+    properties:
+      hibernate:
+        format_sql: true
+  cloud:
+    gateway:
+      routes:
+        - id: contactService
+          uri: lb://contactService
+          predicates:
+            - Path=/api/contact/**
+          filters:
+            - StripPrefix=1
+        - id: mailService
+          uri: lb://mailService
+          predicates:
+            - Path=/api/mail/**
+          filters:
+            - StripPrefix=1
\ No newline at end of file
diff --git a/backend/gateway/src/main/resources/db/migration/V1__add-api-key-schema.sql b/backend/gateway/src/main/resources/db/migration/V1__add-api-key-schema.sql
new file mode 100644
index 0000000..6c6fc1a
--- /dev/null
+++ b/backend/gateway/src/main/resources/db/migration/V1__add-api-key-schema.sql
@@ -0,0 +1,58 @@
+-- 1. Create tables with timestamps correctly
+
+CREATE TABLE api_key
+(
+    id               BIGINT GENERATED BY DEFAULT AS IDENTITY NOT NULL,
+    api_key          VARCHAR(255)                            NOT NULL,
+    type             VARCHAR(255)                            NOT NULL,
+    enabled          BOOLEAN                                 NOT NULL,
+    frontend_only    BOOLEAN                                 NOT NULL,
+    createdDateTime  TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    modifiedDateTime TIMESTAMP NULL,
+    CONSTRAINT pk_api_key PRIMARY KEY (id)
+);
+
+CREATE TABLE api_key_services
+(
+    api_key_id       BIGINT NOT NULL,
+    allowed_service  VARCHAR(255),
+    createdDateTime  TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    modifiedDateTime TIMESTAMP NULL
+);
+
+-- 2. Add constraints
+
+ALTER TABLE api_key
+    ADD CONSTRAINT uc_api_key_key UNIQUE (api_key); -- (fixed: correct column name is api_key)
+
+ALTER TABLE api_key_services
+    ADD CONSTRAINT fk_api_key_services_on_api_key FOREIGN KEY (api_key_id) REFERENCES api_key (id);
+
+-- 3. Function to update modifiedDateTime if any real change occurs
+
+CREATE
+OR REPLACE FUNCTION set_modified_datetime()
+RETURNS TRIGGER AS $$
+BEGIN
+  IF
+(OLD IS DISTINCT FROM NEW) THEN
+    NEW.modifiedDateTime = CURRENT_TIMESTAMP;
+END IF;
+RETURN NEW;
+END;
+$$
+LANGUAGE plpgsql;
+
+-- 4. Triggers to update modifiedDateTime
+
+CREATE TRIGGER trg_set_modified_datetime_api_key
+    BEFORE UPDATE
+    ON api_key
+    FOR EACH ROW
+    EXECUTE FUNCTION set_modified_datetime();
+
+CREATE TRIGGER trg_set_modified_datetime_api_key_services
+    BEFORE UPDATE
+    ON api_key_services
+    FOR EACH ROW
+    EXECUTE FUNCTION set_modified_datetime();
diff --git a/backend/gateway/src/test/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilterTest.java b/backend/gateway/src/test/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilterTest.java
new file mode 100644
index 0000000..e9e1552
--- /dev/null
+++ b/backend/gateway/src/test/java/dev/rheinsw/gateway/filter/ApiKeyGatewayFilterTest.java
@@ -0,0 +1,121 @@
+package dev.rheinsw.gateway.filter;
+
+import dev.rheinsw.gateway.service.ApiKeyValidator;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.springframework.cloud.gateway.filter.GatewayFilterChain;
+import org.springframework.cloud.gateway.route.Route;
+import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
+import org.springframework.mock.http.server.reactive.MockServerHttpRequest;
+import org.springframework.mock.web.server.MockServerWebExchange;
+import org.springframework.test.util.ReflectionTestUtils;
+import reactor.core.publisher.Mono;
+
+import static org.mockito.Mockito.*;
+import static org.junit.jupiter.api.Assertions.*;
+
+class ApiKeyGatewayFilterTest {
+
+    @Mock
+    private ApiKeyValidator apiKeyValidator;
+
+    @Mock
+    private GatewayFilterChain chain;
+
+    private ApiKeyGatewayFilter filter;
+
+    @BeforeEach
+    void setUp() {
+        MockitoAnnotations.openMocks(this);
+        filter = new ApiKeyGatewayFilter(apiKeyValidator);
+
+        // Inject expectedFrontendOrigin manually
+        ReflectionTestUtils.setField(filter, "expectedFrontendOrigin", "https://localhost:3000");
+    }
+
+    private void injectMockRoute(MockServerWebExchange exchange, String routeId) {
+        Route mockRoute = mock(Route.class);
+        when(mockRoute.getId()).thenReturn(routeId);
+        exchange.getAttributes().put(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR, mockRoute);
+    }
+
+    @Test
+    void shouldAllowPublicRequestWithoutValidation() {
+        MockServerHttpRequest request = MockServerHttpRequest.get("/api/public/test").build();
+        MockServerWebExchange exchange = MockServerWebExchange.from(request);
+
+        when(chain.filter(exchange)).thenReturn(Mono.empty());
+
+        filter.filter(exchange, chain).block();
+
+        verify(chain, times(1)).filter(exchange);
+    }
+
+    @Test
+    void shouldAllowValidFrontendApiKey() {
+        MockServerHttpRequest request = MockServerHttpRequest.get("/api/contact/test")
+                .header("Origin", "https://localhost:3000")
+                .header("X-Frontend-Key", "valid-frontend-key")
+                .build();
+        MockServerWebExchange exchange = MockServerWebExchange.from(request);
+        injectMockRoute(exchange, "contactService");
+
+        when(apiKeyValidator.isAuthorized(eq("valid-frontend-key"), eq("contactService"), eq(true))).thenReturn(true);
+        when(chain.filter(exchange)).thenReturn(Mono.empty());
+
+        filter.filter(exchange, chain).block();
+
+        verify(apiKeyValidator).isAuthorized("valid-frontend-key", "contactService", true);
+        verify(chain, times(1)).filter(exchange);
+    }
+
+    @Test
+    void shouldRejectInvalidFrontendApiKey() {
+        MockServerHttpRequest request = MockServerHttpRequest.get("/api/contact/test")
+                .header("Origin", "https://localhost:3000")
+                .header("X-Frontend-Key", "invalid-frontend-key")
+                .build();
+        MockServerWebExchange exchange = MockServerWebExchange.from(request);
+        injectMockRoute(exchange, "contactService");
+
+        when(apiKeyValidator.isAuthorized(eq("invalid-frontend-key"), eq("contactService"), eq(true))).thenReturn(false);
+
+        filter.filter(exchange, chain).block();
+
+        assertEquals(exchange.getResponse().getStatusCode(), org.springframework.http.HttpStatus.UNAUTHORIZED);
+    }
+
+    @Test
+    void shouldAllowValidInternalApiKey() {
+        MockServerHttpRequest request = MockServerHttpRequest.get("/api/contact/test")
+                .header("X-Internal-Auth", "valid-internal-key")
+                .build();
+        MockServerWebExchange exchange = MockServerWebExchange.from(request);
+        injectMockRoute(exchange, "contactService");
+
+        when(apiKeyValidator.isAuthorized(eq("valid-internal-key"), eq("contactService"), eq(false))).thenReturn(true);
+        when(chain.filter(exchange)).thenReturn(Mono.empty());
+
+        filter.filter(exchange, chain).block();
+
+        verify(apiKeyValidator).isAuthorized("valid-internal-key", "contactService", false);
+        verify(chain, times(1)).filter(exchange);
+    }
+
+    @Test
+    void shouldRejectInvalidInternalApiKey() {
+        MockServerHttpRequest request = MockServerHttpRequest.get("/api/contact/test")
+                .header("X-Internal-Auth", "invalid-internal-key")
+                .build();
+        MockServerWebExchange exchange = MockServerWebExchange.from(request);
+        injectMockRoute(exchange, "contactService");
+
+        when(apiKeyValidator.isAuthorized(eq("invalid-internal-key"), eq("contactService"), eq(false))).thenReturn(false);
+
+        filter.filter(exchange, chain).block();
+
+        assertEquals(exchange.getResponse().getStatusCode(), org.springframework.http.HttpStatus.UNAUTHORIZED);
+    }
+}
diff --git a/backend/gateway/src/test/java/dev/rheinsw/gateway/security/ApiKeyValidatorTest.java b/backend/gateway/src/test/java/dev/rheinsw/gateway/security/ApiKeyValidatorTest.java
new file mode 100644
index 0000000..e9b2237
--- /dev/null
+++ b/backend/gateway/src/test/java/dev/rheinsw/gateway/security/ApiKeyValidatorTest.java
@@ -0,0 +1,51 @@
+package dev.rheinsw.gateway.security;
+
+import dev.rheinsw.gateway.model.ApiKey;
+import dev.rheinsw.gateway.model.ApiKeyType;
+import dev.rheinsw.gateway.repository.ApiKeyRepository;
+import dev.rheinsw.gateway.service.ApiKeyValidator;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+import java.util.Set;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+class ApiKeyValidatorTest {
+
+    private final ApiKeyRepository repository = mock(ApiKeyRepository.class);
+    private final ApiKeyValidator validator = new ApiKeyValidator(repository);
+
+    @Test
+    void testAuthorizedFrontendKey() {
+        ApiKey key = ApiKey.builder()
+                .apiKey("frontend-key")
+                .type(ApiKeyType.FRONTEND)
+                .enabled(true)
+                .frontendOnly(true)
+                .allowedServices(Set.of("contactService"))
+                .build();
+
+        when(repository.findByApiKey("frontend-key")).thenReturn(Optional.of(key));
+
+        boolean result = validator.isAuthorized("frontend-key", "contactService", true);
+        assertTrue(result);
+    }
+
+    @Test
+    void testUnauthorizedDueToWrongService() {
+        ApiKey key = ApiKey.builder()
+                .apiKey("internal-key")
+                .type(ApiKeyType.INTERNAL)
+                .enabled(true)
+                .frontendOnly(false)
+                .allowedServices(Set.of("mailService"))
+                .build();
+
+        when(repository.findByApiKey("internal-key")).thenReturn(Optional.of(key));
+
+        boolean result = validator.isAuthorized("internal-key", "contactService", false);
+        assertFalse(result);
+    }
+}
diff --git a/backend/gateway/src/test/resources/application.yml b/backend/gateway/src/test/resources/application.yml
new file mode 100644
index 0000000..bce6082
--- /dev/null
+++ b/backend/gateway/src/test/resources/application.yml
@@ -0,0 +1 @@
+spring.cloud.gateway.mvc-discovery.enabled=false
\ No newline at end of file
diff --git a/backend/placeholder b/backend/placeholder
deleted file mode 100644
index e69de29..0000000
diff --git a/backend/pom.xml b/backend/pom.xml
new file mode 100644
index 0000000..e1847b6
--- /dev/null
+++ b/backend/pom.xml
@@ -0,0 +1,83 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>dev.rheinsw</groupId>
+    <artifactId>rheinsw-backend</artifactId>
+    <version>1.0.0</version>
+    <packaging>pom</packaging>
+
+    <modules>
+        <module>shared</module>
+        <module>discoveryServer</module>
+        <module>gateway</module>
+        <module>services/contactService</module>
+        <module>services/mailService</module>
+    </modules>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <maven.compiler.plugin.version>3.14.0</maven.compiler.plugin.version>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+
+        <!-- Spring-related stuff -->
+        <spring-boot.version>3.4.4</spring-boot.version>
+        <spring-cloud.version>2024.0.1</spring-cloud.version>
+
+        <!-- all the others -->
+        <lombok.version>1.18.38</lombok.version>
+    </properties>
+
+    <dependencyManagement>
+        <dependencies>
+            <!-- Spring Boot BOM -->
+            <dependency>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-dependencies</artifactId>
+                <version>${spring-boot.version}</version>
+                <type>pom</type>
+                <scope>import</scope>
+            </dependency>
+
+            <!-- Spring Cloud BOM -->
+            <dependency>
+                <groupId>org.springframework.cloud</groupId>
+                <artifactId>spring-cloud-dependencies</artifactId>
+                <version>${spring-cloud.version}</version>
+                <type>pom</type>
+                <scope>import</scope>
+            </dependency>
+
+            <!-- Other BOMs or shared deps -->
+            <dependency>
+                <groupId>org.mockito</groupId>
+                <artifactId>mockito-core</artifactId>
+                <version>5.17.0</version>
+                <scope>test</scope>
+            </dependency>
+        </dependencies>
+    </dependencyManagement>
+
+    <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <groupId>org.springframework.boot</groupId>
+                    <artifactId>spring-boot-maven-plugin</artifactId>
+                    <version>${spring-boot.version}</version>
+                </plugin>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-surefire-plugin</artifactId>
+                    <version>3.5.3</version>
+                    <configuration>
+                        <argLine>-Djdk.attach.allowAttachSelf=true</argLine>
+                    </configuration>
+                </plugin>
+            </plugins>
+        </pluginManagement>
+    </build>
+</project>
diff --git a/backend/services/contactService/pom.xml b/backend/services/contactService/pom.xml
new file mode 100644
index 0000000..7759473
--- /dev/null
+++ b/backend/services/contactService/pom.xml
@@ -0,0 +1,100 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>dev.rheinsw</groupId>
+        <artifactId>rheinsw-backend</artifactId>
+        <version>1.0.0</version>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+
+    <artifactId>contactService</artifactId>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven.compiler.plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                    <annotationProcessorPaths>
+                        <path>
+                            <groupId>org.projectlombok</groupId>
+                            <artifactId>lombok</artifactId>
+                            <version>${lombok.version}</version>
+                        </path>
+                    </annotationProcessorPaths>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <!-- Spring Boot starter for REST -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-data-jpa</artifactId>
+        </dependency>
+
+        <!-- Eureka Client -->
+        <dependency>
+            <groupId>org.springframework.cloud</groupId>
+            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.postgresql</groupId>
+            <artifactId>postgresql</artifactId>
+        </dependency>
+
+        <!-- Tools -->
+        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>jakarta.validation</groupId>
+            <artifactId>jakarta.validation-api</artifactId>
+        </dependency>
+
+        <dependency>
+            <groupId>dev.rheinsw</groupId>
+            <artifactId>shared</artifactId>
+            <version>1.0.0</version>
+            <scope>compile</scope>
+        </dependency>
+
+        <!-- test suite -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>
\ No newline at end of file
diff --git a/backend/services/contactService/src/main/java/dev/rheinsw/contactService/ContactServiceApplication.java b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/ContactServiceApplication.java
new file mode 100644
index 0000000..121e60b
--- /dev/null
+++ b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/ContactServiceApplication.java
@@ -0,0 +1,19 @@
+package dev.rheinsw.contactService;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.scheduling.annotation.EnableAsync;
+
+/**
+ * @author Bummsa / BoomerHD / Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+@EnableAsync
+@SpringBootApplication(
+    scanBasePackages = {"dev.rheinsw"}
+)
+public class ContactServiceApplication {
+    public static void main(String[] args) {
+        SpringApplication.run(ContactServiceApplication.class, args);
+    }
+}
\ No newline at end of file
diff --git a/backend/services/contactService/src/main/java/dev/rheinsw/contactService/config/HCaptchaConfig.java b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/config/HCaptchaConfig.java
new file mode 100644
index 0000000..b170535
--- /dev/null
+++ b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/config/HCaptchaConfig.java
@@ -0,0 +1,19 @@
+package dev.rheinsw.contactService.config;
+
+import lombok.Getter;
+import lombok.Setter;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+@Setter
+@Getter
+@Configuration
+@ConfigurationProperties(prefix = "hcaptcha")
+public class HCaptchaConfig {
+    private String secret;
+
+}
diff --git a/backend/services/contactService/src/main/java/dev/rheinsw/contactService/controller/ContactController.java b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/controller/ContactController.java
new file mode 100644
index 0000000..e961aeb
--- /dev/null
+++ b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/controller/ContactController.java
@@ -0,0 +1,114 @@
+package dev.rheinsw.contactService.controller;
+
+import dev.rheinsw.contactService.dto.ContactRequestDto;
+import dev.rheinsw.contactService.model.ContactRequest;
+import dev.rheinsw.contactService.repository.ContactRequestsRepo;
+import dev.rheinsw.contactService.service.HCaptchaValidator;
+import dev.rheinsw.shared.mail.MailServiceClient;
+import lombok.AllArgsConstructor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.*;
+
+import java.time.LocalDateTime;
+
+/**
+ * REST controller to handle contact form submissions.
+ *
+ * @author Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+@RestController
+@AllArgsConstructor
+@RequestMapping("/contact")
+public class ContactController {
+
+    private static final Logger log = LoggerFactory.getLogger(ContactController.class);
+
+    private final HCaptchaValidator captchaValidator;
+    private final ContactRequestsRepo contactRepository;
+    private final MailServiceClient mailServiceClient;
+
+    @PostMapping
+    public ResponseEntity<String> submitContact(@RequestBody ContactRequestDto request) {
+        log.info("Received contact form from: {}", request.name);
+        log.debug("Captcha token: {}", request.captcha);
+        log.info("Message: {}", request.message);
+
+        if (request.email != null) {
+            log.info("Reply to: {} ({})", request.email, request.name);
+        }
+
+        if (!isValidCaptcha(request.captcha)) {
+            log.warn("Captcha verification failed for {}", request.email);
+            return ResponseEntity.status(HttpStatus.FORBIDDEN).body("Captcha verification failed");
+        }
+
+        ContactRequest message = new ContactRequest()
+                .setName(request.name)
+                .setEmail(request.email)
+                .setMessage(request.message)
+                .setCompany(request.company)
+                .setPhone(request.phone)
+                .setWebsite(request.website)
+                .setCaptchaToken(request.captcha)
+                .setSubmittedAt(LocalDateTime.now());
+
+        contactRepository.save(message);
+
+        notifyContactAndTeam(request);
+
+        return ResponseEntity.ok("Contact form submitted successfully");
+    }
+
+    private boolean isValidCaptcha(String captcha) {
+        return "10000000-aaaa-bbbb-cccc-000000000001".equals(captcha) || captchaValidator.isValid(captcha);
+    }
+
+    private void notifyContactAndTeam(ContactRequestDto request) {
+        // User confirmation
+        String userSubject = "Kontaktanfrage erhalten";
+        String userBody = """
+                Hallo %s,
+                
+                wir haben Ihre Nachricht erhalten und melden uns schnellstmöglich bei Ihnen.
+                
+                Ihre Nachricht:
+                %s
+                
+                Mit freundlichen Grüßen
+                Rhein Software
+                """.formatted(request.name, request.message);
+
+        mailServiceClient.sendMail(request.email, userSubject, userBody);
+
+        // Team notification
+        String teamSubject = "Neue Kontaktanfrage";
+        String teamBody = """
+                Neue Kontaktanfrage von: %s
+                E-Mail: %s
+                Unternehmen: %s
+                Telefonnummer: %s
+                Webseite: %s
+                
+                Nachricht:
+                %s
+                """.formatted(
+                request.name,
+                request.email,
+                safe(request.company),
+                safe(request.phone),
+                safe(request.website),
+                request.message
+        );
+
+        mailServiceClient.sendMail("rhein.software@gmail.com", teamSubject, teamBody);
+    }
+
+    private String safe(String value) {
+        return value != null ? value : "-";
+    }
+
+}
diff --git a/backend/services/contactService/src/main/java/dev/rheinsw/contactService/dto/ContactRequestDto.java b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/dto/ContactRequestDto.java
new file mode 100644
index 0000000..fbf3c78
--- /dev/null
+++ b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/dto/ContactRequestDto.java
@@ -0,0 +1,18 @@
+package dev.rheinsw.contactService.dto;
+
+import dev.rheinsw.shared.transport.Dto;
+
+/**
+ * @author Bummsa / BoomerHD / Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+public class ContactRequestDto implements Dto {
+    public String name;
+    public String email;
+    public String message;
+
+    public String company;  // optional
+    public String phone;    // optional
+    public String website;  // optional
+    public String captcha;  // required for hCaptcha validation
+}
\ No newline at end of file
diff --git a/backend/services/contactService/src/main/java/dev/rheinsw/contactService/model/ContactRequest.java b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/model/ContactRequest.java
new file mode 100644
index 0000000..115d36d
--- /dev/null
+++ b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/model/ContactRequest.java
@@ -0,0 +1,95 @@
+package dev.rheinsw.contactService.model;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+import jakarta.validation.constraints.Email;
+import jakarta.validation.constraints.Size;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.time.LocalDateTime;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 22.04.25
+ */
+@Entity
+@Data
+@NoArgsConstructor
+@Table(name = "contact_requests")
+public class ContactRequest {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Size(max = 100)
+    private String name;
+
+    @Size(max = 100)
+    @Email
+    private String email;
+
+    @Size(max = 1000)
+    @Column(length = 1000)
+    private String message;
+
+    @Size(max = 100)
+    private String company;
+
+    @Size(max = 20)
+    private String phone;
+
+    @Size(max = 100)
+    private String website;
+
+    @Size(max = 1024)
+    @Column(name = "captcha_token", length = 1024)
+    private String captchaToken;
+
+    private LocalDateTime submittedAt;
+
+    public ContactRequest setName(String name) {
+        this.name = name;
+        return this;
+    }
+
+    public ContactRequest setEmail(String email) {
+        this.email = email;
+        return this;
+    }
+
+    public ContactRequest setMessage(String message) {
+        this.message = message;
+        return this;
+    }
+
+    public ContactRequest setCompany(String company) {
+        this.company = company;
+        return this;
+    }
+
+    public ContactRequest setPhone(String phone) {
+        this.phone = phone;
+        return this;
+    }
+
+    public ContactRequest setWebsite(String website) {
+        this.website = website;
+        return this;
+    }
+
+    public ContactRequest setCaptchaToken(String captchaToken) {
+        this.captchaToken = captchaToken;
+        return this;
+    }
+
+    public ContactRequest setSubmittedAt(LocalDateTime submittedAt) {
+        this.submittedAt = submittedAt;
+        return this;
+    }
+}
diff --git a/backend/services/contactService/src/main/java/dev/rheinsw/contactService/repository/ContactRequestsRepo.java b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/repository/ContactRequestsRepo.java
new file mode 100644
index 0000000..f71ca2b
--- /dev/null
+++ b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/repository/ContactRequestsRepo.java
@@ -0,0 +1,12 @@
+package dev.rheinsw.contactService.repository;
+
+import dev.rheinsw.contactService.model.ContactRequest;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 22.04.25
+ */
+public interface ContactRequestsRepo extends JpaRepository<ContactRequest, Long> {
+    // empty
+}
diff --git a/backend/services/contactService/src/main/java/dev/rheinsw/contactService/service/HCaptchaValidator.java b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/service/HCaptchaValidator.java
new file mode 100644
index 0000000..426ce25
--- /dev/null
+++ b/backend/services/contactService/src/main/java/dev/rheinsw/contactService/service/HCaptchaValidator.java
@@ -0,0 +1,55 @@
+package dev.rheinsw.contactService.service;
+
+import dev.rheinsw.contactService.config.HCaptchaConfig;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+
+import java.util.Map;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+@Service
+public class HCaptchaValidator {
+    private static final Logger log = LoggerFactory.getLogger(HCaptchaValidator.class);
+
+    private final HCaptchaConfig config;
+    private final RestTemplate restTemplate;
+
+    public HCaptchaValidator(HCaptchaConfig config, RestTemplate restTemplate) {
+        this.config = config;
+        this.restTemplate = restTemplate;
+    }
+
+    public boolean isValid(String token) {
+        if (token == null || token.isBlank()) {
+            log.warn("Captcha token is missing or blank");
+            return false;
+        }
+
+        String secret = config.getSecret();
+        if (secret == null || secret.isBlank()) {
+            log.error("Captcha secret is missing");
+            return false;
+        }
+
+        try {
+            var response = restTemplate.postForObject(
+                    "https://api.hcaptcha.com/siteverify",
+                    new org.springframework.util.LinkedMultiValueMap<String, String>() {{
+                        add("secret", secret);
+                        add("response", token);
+                    }},
+                    Map.class
+            );
+
+            return response != null && Boolean.TRUE.equals(response.get("success"));
+        } catch (Exception e) {
+            log.error("Failed to verify hCaptcha", e);
+            return false;
+        }
+    }
+}
diff --git a/backend/services/contactService/src/main/resources/application.yml b/backend/services/contactService/src/main/resources/application.yml
new file mode 100644
index 0000000..a523a90
--- /dev/null
+++ b/backend/services/contactService/src/main/resources/application.yml
@@ -0,0 +1,31 @@
+server:
+  port: 0  # random port
+
+spring:
+  application:
+    name: contactService
+  datasource:
+    url: jdbc:postgresql://localhost:5432/rheinsw_dev
+    username: rheinsw
+    password: rheinsw
+
+  jpa:
+    hibernate:
+      ddl-auto: none
+    show-sql: true
+    properties:
+      hibernate:
+        format_sql: true
+
+eureka:
+  client:
+    service-url:
+      defaultZone: http://localhost:8761/eureka/
+
+hcaptcha:
+  secret: ES_ff59a664dc764f92870bf2c7b4eab7c5
+
+logging:
+  level:
+    org.hibernate.SQL: DEBUG
+    org.hibernate.type.descriptor.sql.BasicBinder: TRACE
\ No newline at end of file
diff --git a/backend/services/contactService/src/main/resources/db/migration/V1__create_tables.sql b/backend/services/contactService/src/main/resources/db/migration/V1__create_tables.sql
new file mode 100644
index 0000000..254e429
--- /dev/null
+++ b/backend/services/contactService/src/main/resources/db/migration/V1__create_tables.sql
@@ -0,0 +1,12 @@
+CREATE TABLE contact_requests
+(
+    id            SERIAL PRIMARY KEY,
+    name          VARCHAR(100),
+    email         VARCHAR(100),
+    message       VARCHAR(1000),
+    company       VARCHAR(100),
+    phone         VARCHAR(20),
+    website       VARCHAR(100),
+    captcha_token VARCHAR(1024),
+    submitted_at  TIMESTAMP
+);
diff --git a/backend/services/contactService/src/test/java/dev/rheinsw/contactService/controller/ContactControllerTest.java b/backend/services/contactService/src/test/java/dev/rheinsw/contactService/controller/ContactControllerTest.java
new file mode 100644
index 0000000..43432bb
--- /dev/null
+++ b/backend/services/contactService/src/test/java/dev/rheinsw/contactService/controller/ContactControllerTest.java
@@ -0,0 +1,125 @@
+package dev.rheinsw.contactService.controller;
+
+import dev.rheinsw.contactService.dto.ContactRequestDto;
+import dev.rheinsw.contactService.model.ContactRequest;
+import dev.rheinsw.contactService.repository.ContactRequestsRepo;
+import dev.rheinsw.contactService.service.HCaptchaValidator;
+import dev.rheinsw.shared.mail.MailServiceClient;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.*;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+class ContactControllerTest {
+
+    @Mock
+    private HCaptchaValidator hCaptchaValidator;
+
+    @Mock
+    private ContactRequestsRepo repository;
+
+    @Mock
+    private MailServiceClient mailServiceClient;
+
+    @InjectMocks
+    private ContactController controller;
+
+    @BeforeEach
+    void setUp() {
+        MockitoAnnotations.openMocks(this);
+    }
+
+    @Test
+    void submitContact_ShouldReturnSuccess_WhenDevCaptchaTokenUsed() {
+        // Arrange
+        ContactRequestDto request = new ContactRequestDto();
+        request.name = "Test User";
+        request.email = "test@example.com";
+        request.message = "Hello!";
+        request.captcha = "10000000-aaaa-bbbb-cccc-000000000001";
+
+        // Act
+        ResponseEntity<String> response = controller.submitContact(request);
+
+        // Assert
+        assertEquals(HttpStatus.OK, response.getStatusCode());
+        assertEquals("Contact form submitted successfully", response.getBody());
+
+        verify(repository, times(1)).save(any(ContactRequest.class));
+        verify(mailServiceClient, times(2)).sendMail(anyString(), anyString(), anyString());
+        verifyNoInteractions(hCaptchaValidator);
+    }
+
+    @Test
+    void submitContact_ShouldReturnSuccess_WhenCaptchaValid() {
+        // Arrange
+        ContactRequestDto request = new ContactRequestDto();
+        request.name = "Valid User";
+        request.email = "valid@example.com";
+        request.message = "Some message";
+        request.captcha = "real-token";
+
+        when(hCaptchaValidator.isValid("real-token")).thenReturn(true);
+
+        // Act
+        ResponseEntity<String> response = controller.submitContact(request);
+
+        // Assert
+        assertEquals(HttpStatus.OK, response.getStatusCode());
+        assertEquals("Contact form submitted successfully", response.getBody());
+
+        verify(hCaptchaValidator, times(1)).isValid("real-token");
+        verify(repository, times(1)).save(any(ContactRequest.class));
+        verify(mailServiceClient, times(2)).sendMail(anyString(), anyString(), anyString());
+    }
+
+    @Test
+    void submitContact_ShouldReturnForbidden_WhenCaptchaInvalid() {
+        // Arrange
+        ContactRequestDto request = new ContactRequestDto();
+        request.name = "Bot User";
+        request.email = "bot@example.com";
+        request.message = "Spam spam spam";
+        request.captcha = "invalid-token";
+
+        when(hCaptchaValidator.isValid("invalid-token")).thenReturn(false);
+
+        // Act
+        ResponseEntity<String> response = controller.submitContact(request);
+
+        // Assert
+        assertEquals(HttpStatus.FORBIDDEN, response.getStatusCode());
+        assertEquals("Captcha verification failed", response.getBody());
+
+        verify(hCaptchaValidator).isValid("invalid-token");
+        verifyNoInteractions(repository);
+        verifyNoInteractions(mailServiceClient);
+    }
+
+    @Test
+    void submitContact_ShouldHandleNullOptionalFields() {
+        // Arrange
+        ContactRequestDto request = new ContactRequestDto();
+        request.name = "No Company";
+        request.email = "user@example.com";
+        request.message = "Just a message";
+        request.captcha = "real-token";
+        request.company = null;
+        request.phone = null;
+        request.website = null;
+
+        when(hCaptchaValidator.isValid("real-token")).thenReturn(true);
+
+        // Act
+        ResponseEntity<String> response = controller.submitContact(request);
+
+        // Assert
+        assertEquals(HttpStatus.OK, response.getStatusCode());
+        verify(repository).save(any(ContactRequest.class));
+        verify(mailServiceClient, times(2)).sendMail(anyString(), anyString(), anyString());
+    }
+}
diff --git a/backend/services/contactService/src/test/java/dev/rheinsw/contactService/service/HCaptchaValidatorTest.java b/backend/services/contactService/src/test/java/dev/rheinsw/contactService/service/HCaptchaValidatorTest.java
new file mode 100644
index 0000000..0066f81
--- /dev/null
+++ b/backend/services/contactService/src/test/java/dev/rheinsw/contactService/service/HCaptchaValidatorTest.java
@@ -0,0 +1,147 @@
+package dev.rheinsw.contactService.service;
+
+import dev.rheinsw.contactService.config.HCaptchaConfig;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.Mockito;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.web.client.RestTemplate;
+
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.eq;
+
+@ExtendWith(MockitoExtension.class)
+class HCaptchaValidatorTest {
+
+    @Mock
+    private HCaptchaConfig hCaptchaConfig;
+
+    @Mock
+    private RestTemplate restTemplate;
+
+    private HCaptchaValidator validator;
+
+    @BeforeEach
+    void setUp() {
+        validator = new HCaptchaValidator(hCaptchaConfig, restTemplate);
+    }
+
+    @Test
+    void isValid_ShouldReturnFalse_WhenTokenIsNull() {
+        // Arrange
+
+        // Act
+        boolean result = validator.isValid(null);
+
+        // Assert
+        assertFalse(result);
+    }
+
+    @Test
+    void isValid_ShouldReturnFalse_WhenTokenIsBlank() {
+        // Arrange
+
+        // Act
+        boolean result = validator.isValid(" ");
+
+        // Assert
+        assertFalse(result);
+    }
+
+    @Test
+    void isValid_ShouldReturnFalse_WhenSecretIsNull() {
+        // Arrange
+        Mockito.when(hCaptchaConfig.getSecret()).thenReturn(null);
+
+        // Act
+        boolean result = validator.isValid("test-token");
+
+        // Assert
+        assertFalse(result);
+    }
+
+    @Test
+    void isValid_ShouldReturnFalse_WhenSecretIsBlank() {
+        // Arrange
+        Mockito.when(hCaptchaConfig.getSecret()).thenReturn(" ");
+
+        // Act
+        boolean result = validator.isValid("test-token");
+
+        // Assert
+        assertFalse(result);
+    }
+
+    @Test
+    void isValid_ShouldReturnFalse_WhenApiResponseIsNull() {
+        // Arrange
+        Mockito.when(hCaptchaConfig.getSecret()).thenReturn("test-secret");
+        Mockito.when(restTemplate.postForObject(
+                eq("https://api.hcaptcha.com/siteverify"),
+                any(),
+                eq(Map.class)
+        )).thenReturn(null);
+
+        // Act
+        boolean result = validator.isValid("test-token");
+
+        // Assert
+        assertFalse(result);
+    }
+
+    @Test
+    void isValid_ShouldReturnFalse_WhenApiResponseSuccessIsFalse() {
+        // Arrange
+        Mockito.when(hCaptchaConfig.getSecret()).thenReturn("test-secret");
+        Mockito.when(restTemplate.postForObject(
+                eq("https://api.hcaptcha.com/siteverify"),
+                any(),
+                eq(Map.class)
+        )).thenReturn(Map.of("success", false));
+
+        // Act
+        boolean result = validator.isValid("test-token");
+
+        // Assert
+        assertFalse(result);
+    }
+
+    @Test
+    void isValid_ShouldReturnTrue_WhenApiResponseSuccessIsTrue() {
+        // Arrange
+        Mockito.when(hCaptchaConfig.getSecret()).thenReturn("test-secret");
+        Mockito.when(restTemplate.postForObject(
+                eq("https://api.hcaptcha.com/siteverify"),
+                any(),
+                eq(Map.class)
+        )).thenReturn(Map.of("success", true));
+
+        // Act
+        boolean result = validator.isValid("test-token");
+
+        // Assert
+        assertTrue(result);
+    }
+
+    @Test
+    void isValid_ShouldReturnFalse_WhenExceptionIsThrown() {
+        // Arrange
+        Mockito.when(hCaptchaConfig.getSecret()).thenReturn("test-secret");
+        Mockito.when(restTemplate.postForObject(
+                eq("https://api.hcaptcha.com/siteverify"),
+                any(),
+                eq(Map.class)
+        )).thenThrow(new RuntimeException("Simulated Exception"));
+
+        // Act
+        boolean result = validator.isValid("test-token");
+
+        // Assert
+        assertFalse(result);
+    }
+}
diff --git a/backend/services/mailService/pom.xml b/backend/services/mailService/pom.xml
new file mode 100644
index 0000000..feb9bb1
--- /dev/null
+++ b/backend/services/mailService/pom.xml
@@ -0,0 +1,114 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>dev.rheinsw</groupId>
+        <artifactId>rheinsw-backend</artifactId>
+        <version>1.0.0</version>
+        <relativePath>../../pom.xml</relativePath>
+    </parent>
+
+    <artifactId>mailService</artifactId>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven.compiler.plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                    <annotationProcessorPaths>
+                        <path>
+                            <groupId>org.projectlombok</groupId>
+                            <artifactId>lombok</artifactId>
+                            <version>${lombok.version}</version>
+                        </path>
+                    </annotationProcessorPaths>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <!-- Spring Boot starter for REST -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-data-jpa</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-mail</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.cloud</groupId>
+            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <scope>provided</scope>
+        </dependency>
+
+        <!-- https://mvnrepository.com/artifact/jakarta.mail/jakarta.mail-api -->
+        <dependency>
+            <groupId>jakarta.mail</groupId>
+            <artifactId>jakarta.mail-api</artifactId>
+            <version>2.1.3</version>
+        </dependency>
+        <dependency>
+            <groupId>jakarta.validation</groupId>
+            <artifactId>jakarta.validation-api</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-actuator-autoconfigure</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>33.4.0-jre</version>
+            <scope>compile</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>dev.rheinsw</groupId>
+            <artifactId>shared</artifactId>
+            <version>1.0.0</version>
+            <scope>compile</scope>
+        </dependency>
+
+        <!-- test suite -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-junit-jupiter</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+</project>
\ No newline at end of file
diff --git a/backend/services/mailService/src/main/java/dev/rheinsw/mail/MailServiceApplication.java b/backend/services/mailService/src/main/java/dev/rheinsw/mail/MailServiceApplication.java
new file mode 100644
index 0000000..304370e
--- /dev/null
+++ b/backend/services/mailService/src/main/java/dev/rheinsw/mail/MailServiceApplication.java
@@ -0,0 +1,18 @@
+package dev.rheinsw.mail;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 22.04.25
+ */
+@SpringBootApplication(exclude = {
+        org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration.class,
+        org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration.class
+})
+public class MailServiceApplication {
+    public static void main(String[] args) {
+        SpringApplication.run(MailServiceApplication.class, args);
+    }
+}
\ No newline at end of file
diff --git a/backend/services/mailService/src/main/java/dev/rheinsw/mail/controller/MailController.java b/backend/services/mailService/src/main/java/dev/rheinsw/mail/controller/MailController.java
new file mode 100644
index 0000000..5a0601c
--- /dev/null
+++ b/backend/services/mailService/src/main/java/dev/rheinsw/mail/controller/MailController.java
@@ -0,0 +1,33 @@
+package dev.rheinsw.mail.controller;
+
+import dev.rheinsw.shared.mail.dto.MailRequest;
+import dev.rheinsw.mail.service.MailService;
+import jakarta.mail.MessagingException;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.bind.annotation.RequestBody;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 22.04.25
+ */
+@RestController
+@RequestMapping("/mail")
+@RequiredArgsConstructor
+public class MailController {
+
+    private final MailService mailService;
+
+    @PostMapping("/send")
+    public ResponseEntity<String> sendEmail(@RequestBody MailRequest request) {
+        try {
+            mailService.sendEmail(request);
+            return ResponseEntity.ok("Email sent successfully");
+        } catch (MessagingException e) {
+            return ResponseEntity.status(500).body("Failed to send email: " + e.getMessage());
+        }
+    }
+}
diff --git a/backend/services/mailService/src/main/java/dev/rheinsw/mail/service/MailService.java b/backend/services/mailService/src/main/java/dev/rheinsw/mail/service/MailService.java
new file mode 100644
index 0000000..75e6b28
--- /dev/null
+++ b/backend/services/mailService/src/main/java/dev/rheinsw/mail/service/MailService.java
@@ -0,0 +1,33 @@
+package dev.rheinsw.mail.service;
+
+import dev.rheinsw.shared.mail.dto.MailRequest;
+import jakarta.mail.MessagingException;
+import jakarta.mail.internet.MimeMessage;
+import lombok.RequiredArgsConstructor;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.mail.javamail.MimeMessageHelper;
+import org.springframework.stereotype.Service;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 22.04.25
+ */
+@Service
+@RequiredArgsConstructor
+public class MailService {
+
+    private final JavaMailSender mailSender;
+
+    public void sendEmail(MailRequest request) throws MessagingException {
+        MimeMessage message = mailSender.createMimeMessage();
+        MimeMessageHelper helper = new MimeMessageHelper(message, true);
+
+        helper.setFrom("noreply@rhein-software.dev");
+        helper.setTo(request.getTo());
+        helper.setSubject(request.getSubject());
+        helper.setText(request.getMessage(), false);
+
+        mailSender.send(message);
+    }
+
+}
diff --git a/backend/services/mailService/src/main/resources/application.yml b/backend/services/mailService/src/main/resources/application.yml
new file mode 100644
index 0000000..d7cd18f
--- /dev/null
+++ b/backend/services/mailService/src/main/resources/application.yml
@@ -0,0 +1,24 @@
+server:
+  port: 0  # random port
+
+spring:
+  application:
+    name: mailService
+
+  mail:
+    host: smtp.resend.com
+    port: 587
+    username: resend
+    password: re_JnLD5ndg_GnKtXcTqskXm1bg7Wxnghna3
+    properties:
+      mail:
+        smtp:
+          auth: true
+          starttls:
+            enable: true
+    default-encoding: UTF-8
+
+eureka:
+  client:
+    service-url:
+      defaultZone: http://localhost:8761/eureka/
\ No newline at end of file
diff --git a/backend/services/mailService/src/test/java/dev/rheinsw/mail/controller/MailControllerTest.java b/backend/services/mailService/src/test/java/dev/rheinsw/mail/controller/MailControllerTest.java
new file mode 100644
index 0000000..617de0b
--- /dev/null
+++ b/backend/services/mailService/src/test/java/dev/rheinsw/mail/controller/MailControllerTest.java
@@ -0,0 +1,63 @@
+package dev.rheinsw.mail.controller;
+
+import dev.rheinsw.mail.service.MailService;
+import dev.rheinsw.shared.mail.dto.MailRequest;
+import jakarta.mail.MessagingException;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.*;
+import org.springframework.http.ResponseEntity;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.Mockito.*;
+
+class MailControllerTest {
+
+    @Mock
+    private MailService mailService;
+
+    @InjectMocks
+    private MailController mailController;
+
+    private AutoCloseable closeable;
+
+    @BeforeEach
+    void setUp() {
+        closeable = MockitoAnnotations.openMocks(this);
+    }
+
+    @Test
+    void sendEmail_shouldReturnOk_whenEmailSentSuccessfully() throws MessagingException {
+        // Arrange
+        MailRequest request = new MailRequest("user@example.com", "Test Subject", "Message");
+
+        // Act
+        ResponseEntity<String> response = mailController.sendEmail(request);
+
+        // Assert
+        verify(mailService).sendEmail(request);
+        assertEquals(200, response.getStatusCodeValue());
+        assertEquals("Email sent successfully", response.getBody());
+    }
+
+    @Test
+    void sendEmail_shouldReturnServerError_whenMessagingExceptionThrown() throws MessagingException {
+        // Arrange
+        MailRequest request = new MailRequest("user@example.com", "Test Subject", "Message");
+        doThrow(new MessagingException("SMTP failed")).when(mailService).sendEmail(request);
+
+        // Act
+        ResponseEntity<String> response = mailController.sendEmail(request);
+
+        // Assert
+        verify(mailService).sendEmail(request);
+        assertEquals(500, response.getStatusCodeValue());
+        assertTrue(response.getBody().contains("Failed to send email: SMTP failed"));
+    }
+
+    @AfterEach
+    void tearDown() throws Exception {
+        closeable.close();
+    }
+}
diff --git a/backend/services/mailService/src/test/java/dev/rheinsw/mail/service/MailServiceTest.java b/backend/services/mailService/src/test/java/dev/rheinsw/mail/service/MailServiceTest.java
new file mode 100644
index 0000000..5489102
--- /dev/null
+++ b/backend/services/mailService/src/test/java/dev/rheinsw/mail/service/MailServiceTest.java
@@ -0,0 +1,60 @@
+package dev.rheinsw.mail.service;
+
+import dev.rheinsw.shared.mail.dto.MailRequest;
+import jakarta.mail.MessagingException;
+import jakarta.mail.internet.MimeMessage;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.*;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.mail.javamail.MimeMessageHelper;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.*;
+
+class MailServiceTest {
+
+    @Mock
+    private JavaMailSender mailSender;
+
+    @InjectMocks
+    private MailService mailService;
+
+    private AutoCloseable closeable;
+
+    @BeforeEach
+    void setUp() {
+        closeable = MockitoAnnotations.openMocks(this);
+    }
+
+    @Test
+    void sendEmail_shouldSendMessageSuccessfully() throws MessagingException {
+        // Arrange
+        MailRequest request = new MailRequest("user@example.com", "Hello", "This is a test message.");
+        MimeMessage mimeMessage = mock(MimeMessage.class);
+        when(mailSender.createMimeMessage()).thenReturn(mimeMessage);
+
+        // Act & Assert
+        assertDoesNotThrow(() -> mailService.sendEmail(request));
+        verify(mailSender).send(mimeMessage);
+    }
+
+    @Test
+    void sendEmail_shouldThrowMessagingException_whenMailSenderFails() {
+        // Arrange
+        MailRequest request = new MailRequest("user@example.com", "Hello", "This is a test message.");
+        MimeMessage mimeMessage = mock(MimeMessage.class);
+        when(mailSender.createMimeMessage()).thenReturn(mimeMessage);
+        doThrow(new RuntimeException("Simulated failure")).when(mailSender).send(mimeMessage);
+
+        // Act & Assert
+        RuntimeException exception = assertThrows(RuntimeException.class, () -> {
+            mailService.sendEmail(request);
+        });
+
+        assertEquals("Simulated failure", exception.getMessage());
+    }
+
+}
diff --git a/backend/shared/pom.xml b/backend/shared/pom.xml
new file mode 100644
index 0000000..3c204f5
--- /dev/null
+++ b/backend/shared/pom.xml
@@ -0,0 +1,88 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>dev.rheinsw</groupId>
+        <artifactId>rheinsw-backend</artifactId>
+        <version>1.0.0</version>
+    </parent>
+
+    <artifactId>shared</artifactId>
+
+    <properties>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+
+        <jackson-databind.version>2.18.3</jackson-databind.version>
+        <lombok.version>1.18.38</lombok.version>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven.compiler.plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                    <annotationProcessorPaths>
+                        <path>
+                            <groupId>org.projectlombok</groupId>
+                            <artifactId>lombok</artifactId>
+                            <version>${lombok.version}</version>
+                        </path>
+                    </annotationProcessorPaths>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <dependencies>
+        <!-- Spring stuff -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.cloud</groupId>
+            <artifactId>spring-cloud-starter-loadbalancer</artifactId>
+        </dependency>
+
+        <!-- Others -->
+        <!-- https://mvnrepository.com/artifact/jakarta.persistence/jakarta.persistence-api -->
+        <dependency>
+            <groupId>jakarta.persistence</groupId>
+            <artifactId>jakarta.persistence-api</artifactId>
+            <version>3.2.0</version>
+        </dependency>
+
+        <!-- Tests -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-test</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson-databind.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>${lombok.version}</version>
+            <scope>provided</scope>
+        </dependency>
+    </dependencies>
+
+</project>
\ No newline at end of file
diff --git a/backend/shared/src/main/java/dev/rheinsw/shared/entity/BaseEntity.java b/backend/shared/src/main/java/dev/rheinsw/shared/entity/BaseEntity.java
new file mode 100644
index 0000000..f0ee6cf
--- /dev/null
+++ b/backend/shared/src/main/java/dev/rheinsw/shared/entity/BaseEntity.java
@@ -0,0 +1,37 @@
+package dev.rheinsw.shared.entity;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.MappedSuperclass;
+import jakarta.persistence.PrePersist;
+import jakarta.persistence.PreUpdate;
+import lombok.Getter;
+import lombok.Setter;
+
+import java.time.LocalDateTime;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 26.04.25
+ */
+
+@Getter
+@Setter
+@MappedSuperclass
+public abstract class BaseEntity {
+
+    @Column(name = "createdDateTime", nullable = false, updatable = false)
+    private LocalDateTime createdDateTime;
+
+    @Column(name = "modifiedDateTime")
+    private LocalDateTime modifiedDateTime;
+
+    @PrePersist
+    protected void onCreate() {
+        createdDateTime = LocalDateTime.now();
+    }
+
+    @PreUpdate
+    protected void onUpdate() {
+        modifiedDateTime = LocalDateTime.now();
+    }
+}
\ No newline at end of file
diff --git a/backend/shared/src/main/java/dev/rheinsw/shared/mail/MailServiceClient.java b/backend/shared/src/main/java/dev/rheinsw/shared/mail/MailServiceClient.java
new file mode 100644
index 0000000..da2d7ed
--- /dev/null
+++ b/backend/shared/src/main/java/dev/rheinsw/shared/mail/MailServiceClient.java
@@ -0,0 +1,50 @@
+package dev.rheinsw.shared.mail;
+
+import dev.rheinsw.shared.mail.dto.MailRequest;
+import lombok.RequiredArgsConstructor;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.scheduling.annotation.Async;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestTemplate;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 22.04.25
+ */
+@Service
+@RequiredArgsConstructor
+public class MailServiceClient {
+
+    private static final Logger log = LoggerFactory.getLogger(MailServiceClient.class);
+
+    private final RestTemplate restTemplate;
+
+    private static final String MAIL_ENDPOINT = "http://gateway/api/mail";
+
+    @Value("${INTERNAL_API_KEY}")
+    private String internalApiKey;
+
+    @Async
+    public void sendMail(String email, String subject, String userMessage) {
+        MailRequest request = new MailRequest(email, subject, userMessage);
+        postEmail(request);
+    }
+
+    private void postEmail(MailRequest request) {
+        try {
+            HttpHeaders headers = new HttpHeaders();
+            headers.set("X-Internal-Auth", internalApiKey);
+
+            HttpEntity<MailRequest> entity = new HttpEntity<>(request, headers);
+
+            restTemplate.postForEntity(MAIL_ENDPOINT + "/send", entity, String.class);
+        } catch (Exception e) {
+            log.error("Failed to send email to {}: {}", request.getTo(), e.getMessage());
+        }
+    }
+
+}
diff --git a/backend/shared/src/main/java/dev/rheinsw/shared/mail/dto/MailRequest.java b/backend/shared/src/main/java/dev/rheinsw/shared/mail/dto/MailRequest.java
new file mode 100644
index 0000000..299a629
--- /dev/null
+++ b/backend/shared/src/main/java/dev/rheinsw/shared/mail/dto/MailRequest.java
@@ -0,0 +1,20 @@
+package dev.rheinsw.shared.mail.dto;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.Getter;
+import lombok.NoArgsConstructor;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 22.04.25
+ */
+@Data
+@Getter
+@NoArgsConstructor
+@AllArgsConstructor
+public class MailRequest {
+    private String to;
+    private String subject;
+    private String message;
+}
diff --git a/backend/shared/src/main/java/dev/rheinsw/shared/rest/RestTemplateConfig.java b/backend/shared/src/main/java/dev/rheinsw/shared/rest/RestTemplateConfig.java
new file mode 100644
index 0000000..206ce2a
--- /dev/null
+++ b/backend/shared/src/main/java/dev/rheinsw/shared/rest/RestTemplateConfig.java
@@ -0,0 +1,20 @@
+package dev.rheinsw.shared.rest;
+
+import org.springframework.cloud.client.loadbalancer.LoadBalanced;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.client.RestTemplate;
+
+/**
+ * @author Thatsaphorn Atchariyaphap
+ * @since 23.04.25
+ */
+@Configuration
+public class RestTemplateConfig {
+
+    @LoadBalanced
+    @Bean
+    public RestTemplate mailRestTemplate() {
+        return new RestTemplate();
+    }
+}
\ No newline at end of file
diff --git a/backend/shared/src/main/java/dev/rheinsw/shared/transport/Dto.java b/backend/shared/src/main/java/dev/rheinsw/shared/transport/Dto.java
new file mode 100644
index 0000000..e820ef2
--- /dev/null
+++ b/backend/shared/src/main/java/dev/rheinsw/shared/transport/Dto.java
@@ -0,0 +1,10 @@
+package dev.rheinsw.shared.transport;
+
+import java.io.Serializable;
+
+/**
+ * @author Bummsa / BoomerHD / Thatsaphorn Atchariyaphap
+ * @since 21.04.25
+ */
+public interface Dto extends Serializable {
+}
diff --git a/backend/shared/src/test/java/dev/rheinsw/shared/entity/BaseEntityTest.java b/backend/shared/src/test/java/dev/rheinsw/shared/entity/BaseEntityTest.java
new file mode 100644
index 0000000..1b80fe4
--- /dev/null
+++ b/backend/shared/src/test/java/dev/rheinsw/shared/entity/BaseEntityTest.java
@@ -0,0 +1,58 @@
+package dev.rheinsw.shared.entity;
+
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDateTime;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class BaseEntityTest {
+
+    // Dummy entity for testing
+    static class DummyEntity extends BaseEntity {
+    }
+
+    @Test
+    void onCreate_shouldSetCreatedDateTime() {
+        // Arrange
+        DummyEntity entity = new DummyEntity();
+
+        // Act
+        entity.onCreate();
+
+        // Assert
+        assertNotNull(entity.getCreatedDateTime(), "createdDateTime should be set");
+        assertNull(entity.getModifiedDateTime(), "modifiedDateTime should still be null after creation");
+    }
+
+    @Test
+    void onUpdate_shouldSetModifiedDateTime() {
+        // Arrange
+        DummyEntity entity = new DummyEntity();
+
+        // Act
+        entity.onUpdate();
+
+        // Assert
+        assertNotNull(entity.getModifiedDateTime(), "modifiedDateTime should be set");
+        assertNull(entity.getCreatedDateTime(), "createdDateTime should still be null if onCreate() is not called");
+    }
+
+    @Test
+    void onCreate_thenOnUpdate_shouldSetBothTimestamps() throws InterruptedException {
+        // Arrange
+        DummyEntity entity = new DummyEntity();
+
+        // Act
+        entity.onCreate();
+        LocalDateTime created = entity.getCreatedDateTime();
+        Thread.sleep(10); // slight pause to differentiate timestamps
+        entity.onUpdate();
+        LocalDateTime modified = entity.getModifiedDateTime();
+
+        // Assert
+        assertNotNull(created);
+        assertNotNull(modified);
+        assertTrue(modified.isAfter(created), "modifiedDateTime should be after createdDateTime");
+    }
+}
diff --git a/backend/shared/src/test/java/dev/rheinsw/shared/mail/MailServiceClientTest.java b/backend/shared/src/test/java/dev/rheinsw/shared/mail/MailServiceClientTest.java
new file mode 100644
index 0000000..6708ae1
--- /dev/null
+++ b/backend/shared/src/test/java/dev/rheinsw/shared/mail/MailServiceClientTest.java
@@ -0,0 +1,83 @@
+package dev.rheinsw.shared.mail;
+
+import dev.rheinsw.shared.mail.dto.MailRequest;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentCaptor;
+import org.mockito.Captor;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.springframework.http.HttpEntity;
+import org.springframework.web.client.RestTemplate;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.mockito.Mockito.*;
+
+class MailServiceClientTest {
+
+    @Mock
+    private RestTemplate restTemplate;
+
+    @InjectMocks
+    private MailServiceClient mailServiceClient;
+
+    @Captor
+    private ArgumentCaptor<HttpEntity<MailRequest>> httpEntityCaptor;
+
+    private AutoCloseable closeable;
+
+    @BeforeEach
+    void setUp() {
+        closeable = MockitoAnnotations.openMocks(this);
+    }
+
+    @Test
+    void sendMail_shouldSendCorrectRequest() {
+        // Arrange
+        String email = "user@example.com";
+        String subject = "Test Subject";
+        String message = "This is a test message.";
+
+        // Act
+        mailServiceClient.sendMail(email, subject, message);
+
+        // Assert
+        verify(restTemplate).postForEntity(
+                eq("http://gateway/api/mail/send"),
+                httpEntityCaptor.capture(),
+                eq(String.class)
+        );
+
+        MailRequest captured = httpEntityCaptor.getValue().getBody(); // extract the MailRequest
+        assert captured != null;
+        assert captured.getTo().equals(email);
+        assert captured.getSubject().equals(subject);
+        assert captured.getMessage().equals(message);
+    }
+
+    @Test
+    void sendMail_shouldHandleExceptionDuringPost() {
+        // Arrange
+        String email = "user@example.com";
+        String subject = "Test Subject";
+        String message = "This is a test message.";
+
+        doThrow(new RuntimeException("Simulated error")).when(restTemplate).postForEntity(
+                anyString(),
+                any(),
+                eq(String.class)
+        );
+
+        // Act & Assert
+        assertDoesNotThrow(() -> mailServiceClient.sendMail(email, subject, message),
+                "sendMail should handle exception internally and not throw it");
+    }
+
+
+    @AfterEach
+    void tearDown() throws Exception {
+        closeable.close();
+    }
+}
diff --git a/backend/shared/src/test/java/dev/rheinsw/shared/rest/RestTemplateConfigTest.java b/backend/shared/src/test/java/dev/rheinsw/shared/rest/RestTemplateConfigTest.java
new file mode 100644
index 0000000..7d32d69
--- /dev/null
+++ b/backend/shared/src/test/java/dev/rheinsw/shared/rest/RestTemplateConfigTest.java
@@ -0,0 +1,30 @@
+package dev.rheinsw.shared.rest;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.web.client.RestTemplate;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class RestTemplateConfigTest {
+
+    private final RestTemplateConfig restTemplateConfig = new RestTemplateConfig();
+
+    @Test
+    void mailRestTemplate_shouldReturnNonNullRestTemplate() {
+        // Act
+        RestTemplate restTemplate = restTemplateConfig.mailRestTemplate();
+
+        // Assert
+        assertNotNull(restTemplate, "RestTemplate should not be null");
+    }
+
+    @Test
+    void mailRestTemplate_shouldCreateNewInstanceEachTime() {
+        // Act
+        RestTemplate restTemplate1 = restTemplateConfig.mailRestTemplate();
+        RestTemplate restTemplate2 = restTemplateConfig.mailRestTemplate();
+
+        // Assert
+        assertNotSame(restTemplate1, restTemplate2, "Each call should create a new RestTemplate instance");
+    }
+}