docs: function (authenticationRequest) {
  
              var authenticationProviders = this.$providers,
                  provider;
  
              for (var i = 0; i < authenticationProviders.length; i++) {
  
                  provider = authenticationProviders[i];
  
                  if (provider.isResponsibleForAuthenticationRequest(authenticationRequest)) {
                      return provider;
                  }
              }
  
              return null;
  
          }