Why is a refresh token needed? When is it generally used?

The refresh token is used to renew the access token without requiring the user to re-authenticate.

Purpose:

• Access tokens usually have a short lifespan (e.g., 15 minutes) for security reasons.
• When the access token expires, the client can use the refresh token to obtain a new access token.
• This allows maintaining the user session without repeatedly entering login and password.

When used:

• After initial authentication, the server issues a pair of tokens: access token and refresh token.
• The client uses the access token to access protected resources.
• If the access token expires, the client sends the refresh token to the server to get a new access token.

Example scenario:

1. The user logs in and receives an access token (15 minutes) and a refresh token (e.g., 7 days).
2. After 15 minutes, the access token expires.
3. The client automatically sends the refresh token to the server.
4. The server verifies the refresh token and issues a new access token.
5. The user continues working without re-logging in.

This enhances security and user convenience by reducing the risk of long-lived tokens being compromised and decreasing the need to frequently enter passwords.