At the time of writing this book, these are the registered claims:

• iss: The issuer of the token
• sub: The subject information about the party this token is carrying information about
• aud: The audience for the token
• exp: The expiration time, after which the token is considered to be invalid
• nbf: The not before (time), or the time before which the token is considered to be not valid yet
• iat: The time at which the token was issued
• jti: The token ID

Claims can also be categorized as public or private:

• Private: Are those that are defined by users (consumers and producers) of the JWTs. In other words, these are ad hoc claims used for a particular case. As such, care must be taken to prevent collisions.
• Public: Are claims that are either registered with the IANA JSON Web Token Claims Registry (a registry where users can register their claims and thus prevent collisions), or named using a collision resistant name (for instance, by prepending a namespace to its name).

To learn all about claims, please refer to the official website. Now, let's see a couple of code examples involving a subset of these claims.