Rename getOpenIDUsername to getOpenIDIdentity and thread "identity"
through bearer OIDC, Basic-auth parsing, OAuth2Callback, and log fields.
Only fall back (and warn) to the default email claim when the configured
username claim is non-default but missing or empty.
Stop emitting Info logs when groups are absent on only UserInfo or only ID
token claims; log once at Debug when no groups remain after merging both.
Update ClaimMapping docs to mention username and groups claims; fix mTLS
extractIdentity comment typo; clarify GetAuthUserFromRequestSession doc.
Signed-off-by: Andrei Aaron <andreifdaaron@gmail.com>