JWT Authentication and Token Validation in .NET APIs

JWT is often used to carry identity across APIs, but it is not a security silver bullet. Signed does not mean encrypted; payload content can usually be decoded.

Validation Flow

flowchart TD
    A["Receive Authorization header"] --> B["Parse Bearer token"]
    B --> C["Validate signature"]
    C --> D["Validate issuer / audience"]
    D --> E["Validate expiration"]
    E --> F["Read claims"]
    F --> G["Authorization policy"]

Engineering Scenario

Gateways or API services should validate tokens before passing identity and claims to business logic. Business code should not parse unverified tokens itself.

Best Practices

• Manage keys and algorithms centrally.
• Keep claims minimal.
• Keep permission checks in the authorization layer.
• Define expiration, refresh, and revocation strategy.