Summary:

The code changes in this pull request focus on improving the security and reliability of the JWT (JSON Web Token) handling and validation functionality in the cedarling project. The changes span multiple files and address various aspects of JWT processing, including decoding, validation, error handling, and key management.

The key security-related improvements include:

1. Conditional inclusion of the "exp" (expiration) claim in the list of required claims, allowing the application to optionally skip the validation of the expiration claim.
2. Explicit handling of unsupported algorithms, ensuring that the application only processes tokens signed with approved algorithms.
3. Comprehensive error handling and reporting, with the introduction of new error types to provide detailed information about various failure scenarios.
4. Secure key management, including the use of thread-safe and shared-ownership wrappers for the cryptographic keys used in the JWT decoding process.
5. Robust validation of JWT claims, such as "iss", "aud", "sub", "nbf", and "exp", to ensure the integrity and authenticity of the tokens.
6. Graceful handling of missing or unsupported keys in the JWKS (JSON Web Key Set) returned by the trusted issuer.

Overall, the changes in this pull request demonstrate a security-conscious approach to the implementation of JWT-based authentication and authorization in the cedarling project, with a focus on mitigating potential security vulnerabilities and maintaining the reliability and robustness of the system.

Files Changed:

1. jans-cedarling/cedarling/src/jwt/decoding_strategy.rs: Improvements to the JWT decoding and validation logic, including the conditional inclusion of the "exp" claim and the handling of unsupported algorithms.
2. jans-cedarling/cedarling/src/jwt/decoding_strategy/error.rs: Introduction of a new JwtDecodingError enum to handle various error cases that can occur during JWT decoding and validation.
3. jans-cedarling/cedarling/examples/authorize_with_jwt_validation.rs: Demonstration of JWT validation and policy-based authorization using the Cedarling library.
4. jans-cedarling/cedarling/src/init/service_config.rs: Changes to the HTTP client implementation and the handling of trusted issuers and OpenID configurations.
5. jans-cedarling/cedarling/src/jwt/decoding_strategy/key_service/openid_config.rs: Improvements to the thread-safe and shared-ownership handling of the cryptographic keys used for JWT decoding.
6. jans-cedarling/cedarling/src/jwt/jwt_service_config.rs: Refactoring of the JWT service configuration to use an abstraction for the HTTP client.
7. jans-cedarling/cedarling/src/jwt/decoding_strategy/key_service.rs: Implementation of a KeyService for retrieving and caching the cryptographic keys used for JWT decoding.
8. jans-cedarling/cedarling/src/jwt/decoding_strategy/key_service/error.rs: Enhancements to the KeyServiceError enum to handle various error conditions related to key management.
9. jans-cedarling/cedarling/src/jwt/mod.rs: Improvements to the JWT validation logic, including more comprehensive checks on the access_token, id_token, and userinfo_token.
10. jans-cedarling/cedarling/src/jwt/test/with_validation/: Addition of various test cases to ensure the proper handling of different JWT-related error scenarios.