RFC 9493: Subject Identifiers for Security Event Tokens

Security events communicated within Security Event Tokens may support a variety of identifiers to identify subjects related to the event. This specification formalizes the notion of Subject Identifiers as structured information that describes a subject and named formats that define the syntax and semantics for encoding Subject Identifiers as JSON objects. It also establishes a registry for defining and allocating names for such formats as well as the JSON Web Token (JWT) "sub_id" Claim.