JSON Web Token (JWT) are a fundamental part of modern web authentication and authorization systems. It is a compact and self-contained way to represent information between two parties securely. JWTs are often used for authentication and authorization, both on the client and server sides of an application.
JSON Web Tokens (JWTs) are created by encoding a set of claims (payload) along with a header using a cryptographic algorithm. The header typically specifies the token type and signing algorithm (e.g., HMAC, RSA, or ECDSA). The payload contains information such as user ID, roles, or expiration time. The token is then signed using a secret key (for HMAC) or a private key (for RSA/ECDSA) to ensure its integrity.
Once created, the JWT is distributed to the client after authentication, usually via HTTP headers (e.g., Authorization: Bearer <token>) or cookies. The client includes the token in each subsequent request to access protected resources. The server verifies the token’s signature to confirm its authenticity and extracts the payload data for authorization decisions.
JWTs are designed to be stateless, meaning the server does not need to store session data. They can be decoded by splitting the token into its three parts—header, payload, and signature—then base64-decoding the first two sections. The signature is verified to ensure the token has not been tampered with before trusting its claims.
Decoding a JWT itself does not pose a security risk because JWTs are encoded using Base64Url, which is easily reversible and not encrypted. Anyone can decode a JWT to see its payload and header. However, the real security concern arises if sensitive information (such as passwords, secrets, or personally identifiable information) is stored in the payload.
Therefore, nobody should decode a JWT on a public website. Instead they should develop their own JWT token decoder and use it behind firewalls. In Group IV Technologies we have developed our own JWT token decoder using React. Input and output might look like this:
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