Username and Password Authentication Using JWT

JWT (JSON Web Token) is a self-contained token that securely encodes information between parties as a JSON object. One of JWT's primary use cases is for authentication in web applications or APIs.

User authentication using JWT begins with the client submitting their username and password. Assuming the user exists and the provided credentials are valid, the next step is to issue an access token and a refresh token by signing the username along with metadata, such as an expiration date, using a server private key.

The client can then commence using the access token as part of their requests for protected resources. The resource access flow starts with the client attaching their access token in the "Authorization" header. The server verifies the access token with its corresponding server private key and permits the request to proceed if the provided access token is valid.

Access tokens have a short lifespan. Once they expire, the client must use the refresh token, which has a much longer lifespan, to obtain a new access token. The refresh token was originally set in the browser's cookie during the initial authentication and is accessible to the server with every request. When the client wishes to refresh their access token, the server verifies their refresh token. Upon successful verification, the server signs a new access token by encrypting the username with a new expiration date using the server private key.