![]() The iat claim is set in the JWT with a timestamp when the current timestamp is less than that.The nbf claim is set in the JWT with a timestamp when the current timestamp is less than that.The signature is invalid, which means the data was tampered with!.The header or the payload is not a valid JSON string.The number of segments provided did not match the standard three as described earlier.If the process to decode the JWT fails, it could be that: If the token isn’t valid because, for example, the token has expired, the user will be sent an HTTP 401 Unauthorized header, and the script will exit. If we decode the example above, we’ll have the following JSON strings: These three are digitally signed ( not encrypted) using the algorithm specified in the JWT’s header. The JWT’s signature is a combination of three things: The signature ensures the JWT’s integrity so that consumers can verify it hasn’t been tampered with by a malicious actor. The JWT’s signature is a cryptographic mechanism designed to secure the JWT’s data with a digital signature unique to the contents of the token. They’re only for use between two parties: a producer and a consumer. However, they can’t be the same as registered claims, or claims of already existing public claims. Public claims can be defined as you see fit. exp: a timestamp of when the token should cease to be valid.nbf: a timestamp of when the token should start being considered valid.Can be a domain name and can be used to discard tokens from other applications. ![]() iss: a string containing the name or identifier of the issuer.key: a unique string, which could be used to validate a token, but goes against not having a centralized issuer authority.You can find a list of them in the JWT’s RFC. There are three types of claims: registered, public, and private. It contains some standard fields, which are referred to as “claims”. It’s also a Base64, URL-encoded JSON string. These algorithms should be used when a shared secret is impractical or other parties only need to verify the integrity of the token. Otherwise, anyone can create a valid token.Īn asymmetric algorithm uses a private key to sign the token and a public key to verify it. It’s essential that you make sure only the creator and consumer knows the secret. The key is shared between the creator of the JWT and the consumer of it. The algorithm can be either symmetric or asymmetric.Ī symmetric algorithm uses a single key to both create and verify the token. It specifies which cryptographic algorithm was used to generate the signature, and the token’s type, which is always set to JWT. However, if you look more closely, there are three separate strings. As such, it may not seem very different from an API key. ![]() Here is a sample JWT: 4TCoh36FU7XhUbcskygS81HE1uHLf0EĪt first glance, it appears that the string is just random groups of characters concatenated with a period or dot character. Other storage media and special configurations have to be implemented - and be done so in full awareness of their implications. Since session files are, by default, stored on the file system, it’s hard to have a distributed or clustered infrastructure for high availability applications - ones that require the use of technologies such as load balancers and clustered servers. If you have a large number of users, you can end up with a slow server unless you use alternative session storage options, such as Memcached and Redis. The same goes for every time the application sends a session cookie.
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