OpenID logoThe OpenID Connect working group has published the initial version of the OpenID Connect Token Hash Algorithm Implementer’s Guide 1.0. Thanks to Filip Skokan for writing this. Quoting from the Abstract:

This OpenID Connect Token Hash Algorithm Implementer’s Guide 1.0 identifies the hash algorithms to use when calculating OpenID Connect ID Token hash claims, such as at_hash and c_hash, Financial-grade API s_hash, and profile-defined token hash claims, for JWS algorithms whose hash function is not completely determined by the algorithm identifier in JSON Web Algorithms (JWA) [JWA].

This guide records implementation guidance for existing and registered JWS algorithm identifiers. It is intended to remain open for maintenance and is not intended to advance to Final Specification status.

For instance, it specifies that SHA-512 is to be used with Ed25519 and SHAKE256 is to be used with the ML-DSA algorithms. Note that decisions remain to be made for the SLH-DSA algorithms.

The spec is listed in the set of OpenID Connect Implementer’s Guides.