How Angular HTTP Interceptors Automate JWT Auth and Token Refresh

A developer has shared a technique for managing JWT authentication in Angular applications using an HTTP interceptor. The interceptor automatically attaches an access token to every outgoing API request, eliminating the need to add authorization headers manually in each service. When a request returns a 401 Unauthorized error, the interceptor attempts to silently refresh the access token using a stored refresh token before retrying the original request. If the refresh token is also expired or invalid, the user's session data is cleared and they are redirected to the login page. A key safeguard prevents infinite loops by detecting when the failed request is itself the refresh endpoint, triggering an immediate logout instead of another refresh attempt.