GUACAMOLE-839: Support deferred retrieval of authentication parameters.

guacamole/src/main/frontend/src/app/auth/service/authenticationService.js

@@ -26,9 +26,11 @@
  * result of authentication operations:
  *
  *  "guacLoginPending"
- *      An authentication request was submitted and we are awaiting the result.
+ *      An authentication request is being submitted and we are awaiting the
- *      This event receives an object containing the HTTP parameters submitted
+ *      result. The request may not yet have been submitted if the parameters
- *      as its sole parameter.
+ *      for that request are not ready. This event receives a promise that
+ *      resolves with the HTTP parameters that were ultimately submitted as its
+ *      sole parameter.
  *
  *  "guacLogin"
  *      Authentication was successful and a new token was created. This event
@@ -66,6 +68,7 @@ angular.module('auth').factory('authenticationService', ['$injector',
     var Error                = $injector.get('Error');
 
     // Required services
+    var $q                  = $injector.get('$q');
     var $rootScope          = $injector.get('$rootScope');
     var localStorageService = $injector.get('localStorageService');
     var requestService      = $injector.get('requestService');
@@ -172,28 +175,37 @@ angular.module('auth').factory('authenticationService', ['$injector',
      * 
      * If a token is provided, it will be reused if possible.
      * 
-     * @param {Object} parameters 
+     * @param {Object|Promise} parameters
-     *     Arbitrary parameters to authenticate with.
+     *     Arbitrary parameters to authenticate with. If a Promise is provided,
+     *     that Promise must resolve with the parameters to be submitted when
+     *     those parameters are available, and any error will be handled as if
+     *     from the authentication endpoint of the REST API itself.
      *
      * @returns {Promise}
      *     A promise which succeeds only if the login operation was successful.
      */
     service.authenticate = function authenticate(parameters) {
 
-        // Notify that a fresh authentication request is being submitted
+        // Coerce received parameters object into a Promise, if it isn't
+        // already a Promise
+        parameters = $q.resolve(parameters);
+
+        // Notify that a fresh authentication request is underway
         $rootScope.$broadcast('guacLoginPending', parameters);
 
-        // Attempt authentication
+        // Attempt authentication after auth parameters are available ...
+        return parameters.then(function requestParametersReady(requestParams) {
+
             return requestService({
                 method: 'POST',
                 url: 'api/tokens',
                 headers: {
                     'Content-Type': 'application/x-www-form-urlencoded'
                 },
-            data: $.param(parameters)
+                data: $.param(requestParams)
             })
 
-        // If authentication succeeds, handle received auth data
+            // ... if authentication succeeds, handle received auth data ...
             .then(function authenticationSuccessful(data) {
 
                 var currentToken = service.getCurrentToken();
@@ -221,9 +233,11 @@ angular.module('auth').factory('authenticationService', ['$injector',
                 // Authentication was successful
                 return data;
 
+            });
+
         })
 
-        // If authentication fails, propogate failure to returned promise
+        // ... if authentication fails, propogate failure to returned promise
         ['catch'](requestService.createErrorCallback(function authenticationFailed(error) {
 
             // Notify of generic login failure, for any event consumers that