How to authenticate using JSON Web Tokens in cURL

JSON Web Tokens (JWTs) provide a compact, self-contained way to transmit information between parties as JSON objects securely. They are widely used for authentication and authorization in modern web applications and APIs. JWTs are particularly useful in single sign-on (SSO) and securing RESTful services, offering a streamlined approach to handling user identity and permissions.

To use JWTs for authentication, a client obtains a token by submitting valid credentials to an authentication server. Upon validation, the server issues a JWT, which the client includes in the Authorization header as a Bearer token for subsequent requests to access protected resources.

cURL simplifies the use of JWTs. It supports obtaining the JWT from an authentication endpoint, which can then be saved locally. You can then use the token by retrieving it from the file and sending it in the Authorization header of a request. It also supports refreshing the JWT if it expires, enabling seamless interaction with secure APIs.

1. Open the terminal.
2. Obtain your JWT, typically from a login endpoint or your authentication provider.

   $ curl -d '{"username":"user", "password":"pass"}' -H "Content-Type: application/json" http://example.com/auth/login

3. Include the JWT in the Authorization header of your cURL request. Use the Bearer schema.

   $ curl -H "Authorization: Bearer <your_jwt_here>" http://example.com/api/protected

   Replace <your_jwt_here> with your actual JWT. The Bearer authentication scheme is used as a prefix to the token.

4. Use the -v or --verbose option if you need to debug or verify that the JWT is being sent correctly.

   $ curl -H "Authorization: Bearer <your_jwt_here>" http://example.com/api/protected -v

   The verbose option will display the request headers, allowing you to confirm that the Authorization header is included correctly.

5. Handle potential errors in your request, such as 401 Unauthorized or 403 Forbidden, by ensuring your JWT is valid and has the correct permissions.
6. Refresh your JWT if it expires. Most JWTs have an expiration time, and you may need to obtain a new token.

   $ curl -d '{"refreshToken":"<your_refresh_token_here>"}' -H "Content-Type: application/json" http://example.com/auth/refresh

   Replace <your_refresh_token_here> with your actual refresh token. Some systems provide a refresh token alongside the JWT for this purpose.

7. Use cURL's built-in features to automate or script these authentication steps for regular API interaction or testing purposes.