Learn how JWT sections, claims, signatures, validation, and expiry fit together in an authentication system.
Three compact sections
A common signed JWT contains a Base64URL-encoded header, a Base64URL-encoded payload, and a signature separated by dots. The payload is readable and should not contain secrets.
Verification establishes integrity
Signature verification checks that the signed bytes match a trusted key and algorithm. Applications must additionally validate issuer, audience, time claims, token type, and their own authorization rules.
Expiry is only one rule
An unexpired token can still be invalid because it has the wrong audience, an untrusted issuer, a future not-before time, a revoked session, or inadequate permissions.
Next step: Use the related browser tool to apply these ideas and verify the result in its destination system.
Great guide! Does local browser execution work for large files over 50MB?