Add optional userInfo param to registerWithProvider (#915)

* Add optional userInfo param to registerWithProvider

* Fixes per PR comments

docs/sync.js

@@ -1,3 +1,4 @@
+import {stringify} from 'ini';
 ////////////////////////////////////////////////////////////////////////////
 //
 // Copyright 2016 Realm Inc.
@@ -139,15 +140,17 @@ class User {
 	static login(server, username, password, callback) {}
 
 	/**
-	 * Login a sync user using an external login provider.
+	 * Register/login a sync user using an external login provider.
 	 * @param {string} server - authentication server
-	 * @param {string} provider - The provider type
-	 * @param {string} providerToken - The access token for the given provider
+   * @param {object} options - options, containing the following:
+	 * @param {string} options.provider - The provider type
+	 * @param {string} options.providerToken - The access token for the given provider
+   * @param {object} [options.userInfo] - A map containing additional data required by the provider
 	 * @param {function(error, User)} callback - called with the following arguments:
 	 *   - `error` - an Error object is provided on failure
 	 *   - `user` - a valid User object on success
 	 */
-	static registerWithProvider(server, provider, providerToken, callback) {}
+	static registerWithProvider(server, options, callback) {}
 
 	/**
 	 * Register a sync user with username and password.

lib/user-methods.js

@@ -157,11 +157,28 @@ module.exports = {
             }, callback);
         },
 
-        registerWithProvider(server, provider, providerToken, callback) {
-            _authenticate(this, server, { 
-                provider: provider, 
-                data: providerToken
-            }, callback);
+        registerWithProvider(server, options, callback) {
+
+            // Compatibility with previous signature: 
+            // registerWithProvider(server, provider, providerToken, callback)
+            if (arguments.length === 4) {
+                options = {
+                    provider: arguments[1],
+                    providerToken: arguments[2]
+                };
+                callback = arguments[3];    
+            }
+
+            let reqOptions = {
+                provider: options.provider,
+                data: options.providerToken,
+            };
+
+            if (options.userInfo) {
+                reqOptions.user_info = options.userInfo;
+            }
+
+            _authenticate(this, server, reqOptions, callback);
         },
 
         _refreshAccessToken: refreshAccessToken