Can JWT signature be decoded?

JWTs can be either signed, encrypted or both. If a token is signed, but not encrypted, everyone can read its contents , but when you don’t know the private key, you can’t change it. Otherwise, the receiver will notice that the signature won’t match anymore.

jwt.verify(token, secretOrPublicKey, [options, callback]) (Synchronous) If a callback is not supplied, function acts synchronously. Returns the payload decoded if the signature is valid and optional expiration, audience, or issuer are valid . If not, it will throw the error.

Yes, the user can decrypt it and see the data , but if they modify it, when it gets back to the server it will not match and therefore be invalid.