def valid_credentials?(kind, *credentials)
      found_username =
        (all_credentials(kind).detect { |c| c[:credentials] == credentials } || {})[:username]
      @users[found_username]
    end
def valid_credentials?(kind, *credentials)
      found_username =
        (all_credentials(kind).detect { |c| c[:credentials] == credentials } || {})[:username]
      @users[found_username]
    end
AUTHORITY API IMPLEMENTATION

 Verifies the credentials against the set provided by calls to
 {#valid_credentials!} and {#load!}.  Supports all kinds.

 @return [Aker::User, nil]