To securely pass user identity between REST services, the following techniques are widely used to ensure security, integrity, and seamless communication:
1. Use JSON Web Tokens (JWT)
- How it works:
- Service A generates a signed JWT containing user identity (e.g., user ID, roles, or permissions) and sends it to Service B.
- The token is signed using a shared secret (HMAC) or private key (RSA/ECDSA), ensuring it cannot be tampered with.
- Benefits:
- Lightweight and self-contained.
- Easy to verify without needing to query a central server.
- Best Practices:
- Use HTTPS to encrypt the transmission.
- Set an expiration time in the exp claim to limit token validity.
- Include a unique jti (JWT ID) to prevent token reuse (replay attacks).
2. OAuth 2.0 Access Tokens
- How it works:
- Service A obtains an OAuth access token on behalf of the user from an authorization server.
- It passes the token to Service B in the Authorization header (e.g., Bearer <token>).
- Service B validates the token with the authorization server or a public key (for signed tokens like JWT).
- Benefits:
- Decouples authentication from the services.
- Supports granular permissions through scopes.
- Best Practices:
- Use short-lived access tokens and refresh tokens.
- Limit token scope to necessary actions for the service.
3. API Gateway
- How it works:
- An API gateway acts as an intermediary, authenticating the user and forwarding their identity to downstream services.
- User identity can be passed as headers, JWT, or custom claims added by the gateway.
- Benefits:
- Simplifies identity propagation.
- Centralized security and monitoring.
- Best Practices:
- Ensure the API gateway is configured to sanitize inputs and enforce strict security policies.
4. Mutual TLS (mTLS)
- How it works:
- Both services authenticate each other using client certificates during the TLS handshake.
- User identity can be embedded in the certificate or passed securely in the request.
- Benefits:
- Provides strong authentication and encryption.
- Best Practices:
- Use certificate pinning to prevent impersonation.
- Rotate certificates regularly.
5. Signed HTTP Headers
- How it works:
- Service A includes user identity in HTTP headers, digitally signed to prevent tampering.
- Service B validates the signature using a shared secret or public key.
- Benefits:
- Simple for lightweight use cases.
- Best Practices:
- Sign headers using robust algorithms (e.g., HMAC-SHA256).
- Include a timestamp to prevent replay attacks.
