Senior Engineer And Token Security

Senior engineer - token security in London

Rate: £550 day outside IR35
Start date: ASAP
End date: 18/12/2026
Clearance: Active SC Clearance
Location: Remote/Hybrid (UK-based)

Responsibilities

• Design and implement OAuth 2.0 Token Exchange (RFC 8693) capabilities.
• Develop secure 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) standards.

Essential

• OAuth 2.0 standards.
• Proven 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 access controls.

Delegation and token management

• Experience implementing:
  • Token down-scoping
  • Audience restriction (aud)
  • Actor and subject claims handling
• Experience designing secure token lifecycle management strategies including:
  • Token caching
  • Token renewal
  • Revocation patterns

Familiar with

• CDDO Secure by Design principles.
• Experience with cloud security architectures.
• Knowledge of API gateways, service meshes, and federated platforms.