JWT Security Relies on Key Management and Algorithm Restriction

JWT authenticity depends solely on a secure signature generated by a private key held only by the issuer. Verifiers use a published public key, identified by a key ID within the token, to check this signature. Keys must be rotated carefully by publishing the new public key before retiring the old one to avoid invalidating active tokens. Developers must explicitly allow specific signing algorithms and never trust the 'alg' field in the token header, as failure to do so can lead to severe security breaches.