Spring Boot

Integrating Keycloak with Spring Boot for OAuth2 resource server protection is one of the most searched tasks in the IAM developer community — yet most tutorials stop at “hello world” level. This guide covers production-grade integration: JWT validation, Keycloak realm role extraction, multi-tenant setups, and integration testing strategies. Clone the companion repo: All working code in this guide is available at github.com/IAMDevBox/keycloak-spring-boot-oauth2 — includes Docker Compose for Keycloak, complete Spring Boot 3.x application, and integration tests with Testcontainers. ...

Visual Overview: sequenceDiagram participant User participant App as Client App participant AuthServer as Authorization Server participant Resource as Resource Server User->>App: 1. Click Login App->>AuthServer: 2. Authorization Request AuthServer->>User: 3. Login Page User->>AuthServer: 4. Authenticate AuthServer->>App: 5. Authorization Code App->>AuthServer: 6. Exchange Code for Token AuthServer->>App: 7. Access Token + Refresh Token App->>Resource: 8. API Request with Token Resource->>App: 9. Protected Resource Proof Key for Code Exchange (PKCE) has become a standard security enhancement to the OAuth 2.0 Authorization Code Flow—especially in public clients like mobile and single-page applications. But PKCE isn’t just for frontend apps. When combined with a stateless backend built with Kotlin and Spring Boot, it strengthens your security posture, particularly when you’re avoiding client secrets. ...