UserLookup

Resolves a username to BasicUserDetails carrying the caller's own identity.

Returns the stored BasicUserDetails (encoded password, identity, and roles to attach on success), or null when the username is unknown. Must return null for unknown users rather than throw. BasicAuthenticator compares BasicUserDetails.encodedPassword against the caller's raw password via PasswordEncoder, then attaches BasicUserDetails.identity and BasicUserDetails.roles on the request — the encoded password itself never reaches the request. Register via the basicAuth { } block (userLookup).