Spring Oauth2 Resource Server

spring-oauth2-resource-server

Wire a Spring Boot application to accept and validate OAuth2/OIDC JWT access tokens (resource-server role). This covers protecting an API with bearer tokens. It does not configure the login/authorization-code flow (that is the client role) or opaque-token introspection.

Provider-agnostic: it is driven entirely by an issuer-uri, so it works with Keycloak, Auth0, Okta, Cognito, Entra ID, or any OIDC-compliant authorization server.

Before you start

Discover the target project's shape rather than assuming it (use Glob/Grep):

• Build tool: build.gradle / build.gradle.kts vs pom.xml, and whether Gradle uses a version catalog (gradle/libs.versions.toml).
• Spring Boot version: read it from the build file. It changes two test imports (see references/dependencies.md).
• Base package: the package under src/main/java/... holding the main @SpringBootApplication class. New classes go in a config subpackage of it.
• Config format: application.yml vs application.properties.

Then gather the values to plug in:

• issuer-uri: the OIDC issuer base URL.
• audience: the value expected in the token's aud claim (usually the API's client id / identifier).
• allowed CORS origins: the browser origins that call this API.

Steps

Reference files live in this skill's references/ directory. Copy them into the project, then substitute com.example.app with the real base package and adjust placeholders.

1. Add dependencies. Add spring-boot-starter-oauth2-resource-server (main) and spring-security-test (test) using the snippet in references/dependencies.md that matches the project's build tool.

2. Add SecurityConfig. Copy references/SecurityConfig.java into <base-package>/config/. It defines a stateless filter chain (anyRequest().authenticated(), oauth2ResourceServer().jwt()), CORS scoped to configured origins, and a JwtDecoder that adds audience validation on top of the default signature/issuer/expiry checks.

3. Add AudienceValidator. Copy references/AudienceValidator.java into the same config/ package. Recommended: without it, a token minted for any other client of the same issuer is accepted. If you deliberately do not want audience checking, omit both this class and the jwtDecoder bean, and Spring auto-configures a decoder from issuer-uri alone.

4. Add config properties. Merge references/application.yml into the project's config (or translate to .properties), filling in issuer-uri, audience, and allowed-origins. Keep them env-overridable.

5. Add a test. Copy references/SecurityConfigTest.java, point @WebMvcTest at a protected controller, and set the request path. It proves anonymous requests get 401 and a valid JWT is accepted, without a live issuer (the JwtDecoder is mocked).

6. Verify. Build and run the test suite (./gradlew test or mvn test). Then confirm at runtime: a request with no token returns 401, and a request with a valid bearer token from the issuer returns 200.

Notes

• CSRF is disabled in the template because a token-authenticated API holds no server-side session or auth cookie. If this same app also serves cookie/session-authenticated endpoints, do not blanket-disable CSRF.
• Roles/scopes: this sets up authentication (valid token required). To authorize by scope or role, add a JwtAuthenticationConverter and .hasAuthority(...) rules; out of scope here.
• Follow-up: run the security-reviewer agent afterward to audit the result (audience, CORS, issuer, token handling).