OPENAM-13434 but for userinfo_signing_alg_values_supported
Optional doesn't mean we don't have to implement it, it means if it's empty, it's because the user info can't be signed. It's not the case of AM, we do support this feature.
This is also applicable for 'userinfo_encryption_alg_values_supported' and 'userinfo_encryption_enc_values_supported'.
call the wellknown:
In my OB setup, I would expect AM to return ["RS256","PS256"]