JWT Authentication Explained: How Tokens Replace Passwords After Login

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JWT (JSON Web Token) is a widely used authentication method in modern backend development that eliminates the need to repeatedly send passwords with every server request. When a user logs in with valid credentials, the server generates a JWT and sends it back to the client, which then includes it in all subsequent requests. The token consists of three parts — a header describing the algorithm, a payload carrying user details like ID and role, and a cryptographic signature that detects any tampering. Because the signature invalidates the token if it is altered, the server can trust its authenticity without maintaining server-side sessions. This stateless design makes JWT particularly well-suited for REST APIs and applications that need to scale across multiple servers.

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