code: function (realm, providerFactory, config) {
                  var provider = $injector.invoke(providerFactory);
                  provider.setConfig(config);
                  provider.setRealm(realm);
                  authProviders.push(provider);
              }
docs: @ngdoc function
  @name w20CoreSecurity.service:AuthenticationService#addProvider
  @methodOf w20CoreSecurity.service:AuthenticationService
  @param {String} realm The realm
  @param {Object} providerFactory An injectable AngularJS factory that act as a provider for authentication.
  This factory should return an object with a setConfig(config) and setRealm(realm) methods.
  @param {Object} config A configuration object with a **authorization** property url and a **authentication** property url
  
  @description
  
  Add an authentication provider which can then be used by any security realm definition.