Senior Engineer - Identity and Token SecurityRate: 550 day Outside IR35Start Date: ASAPEnd Date: 18/12/2026Active SC ClearanceLocation: Remote/Hybrid (UK-based)ResponsibilitiesDesign and implement OAuth 2.0 Token Exchange (RFC 8693) capabilities.Develop secure identity delegation and propagation patterns across distributed services.Implement token down-scoping and audience restriction mechanisms aligned to least-privilege principles.Design secure service-to-service authentication frameworks within zero-trust environments.Build and maintain robust JWT validation and cryptographic trust chains.Integrate applications and services using OpenID Connect (OIDC) standardsEssential:OAuth 2.0 and Identity StandardsProven hands-on implementation experience with OAuth 2.0 Token Exchange (RFC 8693).Strong understanding of OpenID Connect (OIDC) core specifications.Expert-level understanding of JWT (RFC 7519).Experience signing, validating and encrypting tokens using JWS and JWE.Strong knowledge of JWKS endpoints and automated key rotation strategies.Understanding of secure alternatives to shared-secret authentication mechanisms.Experience securing service-to-service communication within distributed microservice architectures.Understanding of zero-trust security principles.Knowledge of secure transit-layer protection and identity-based access controls.Identity Delegation and Token ManagementExperience implementing:Token down-scopingAudience restriction (aud)Actor and Subject claims ..... full job details .....