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I generated a JWT and there are some claims which I understand well, but there is a claim called kid in header. Does anyone know what it means?
I generated the token using auth0.com
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Key Id mainly refers to a Secret that can be retrieved and used to validate the signed JWT. - Mostly it is just a random guid that is stored as a secret Id. It should be provided by the generator of the JWT so that a Validator can retrieve the correct secret based on the "kid" to validate the signed JWT token.
In a JWT, a claim appears as a name/value pair where the name is always a string and the value can be any JSON value. Generally, when we talk about a claim in the context of a JWT, we are referring to the name (or key). For example, the following JSON object contains three claims ( sub , name , admin ):
kid" (Key ID) Parameter The "kid" (key ID) parameter is used to match a specific key. This is used, for instance, to choose among a set of keys within a JWK Set during key rollover. The structure of the "kid" value is unspecified.
The name of the key (key id), which is an identifier generated by the resource server. It is RECOMMENDED that the authorization server generates this key id by computing a hash over the access_token, for example using SHA-1, and to encode it in a base64 format. (
kid is an optional header claim which holds a key identifier, particularly useful when you have multiple keys to sign the tokens and you need to look up the right one to verify the signature.
Once a signed JWT is a JWS, consider the definition from the RFC 7515:
4.1.4. "kid" (Key ID) Header Parameter
The
kid(key ID) Header Parameter is a hint indicating which key was used to secure the JWS. This parameter allows originators to explicitly signal a change of key to recipients. The structure of thekidvalue is unspecified. Its value MUST be a case-sensitive string. Use of this Header Parameter is OPTIONAL.When used with a JWK, the
kidvalue is used to match a JWKkidparameter value.
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