Fixed issue #64.

Author: killme2008

lib/user.js

@@ -640,6 +640,40 @@
       return user.logIn(options);
     },
 
+    /**
+     * Logs in a user with a session token. On success, this saves the session
+     * to disk, so you can retrieve the currently logged in user using
+     * <code>current</code>.
+     *
+     * <p>Calls options.success or options.error on completion.</p>
+     *
+     * @param {String} sessionToken The sessionToken to log in with.
+     * @param {Object} options A Backbone-style options object.
+     * @return {AV.Promise} A promise that is fulfilled with the user when
+     *     the login completes.
+     */
+    become: function(sessionToken, options) {
+      options = options || {};
+
+      var user = AV.Object._create("_User");
+      return AV._request(
+          "users",
+          "me",
+          null,
+          "GET",
+          {
+            useMasterKey: options.useMasterKey,
+            session_token: sessionToken
+          }
+      ).then(function(resp, status, xhr) {
+          var serverAttrs = user.parse(resp, status, xhr);
+          user._finishFetch(serverAttrs);
+          user._handleSaveResult(true);
+          return user;
+
+      })._thenRunCallbacks(options, user);
+    },
+
     /**
      * Logs in a user with a mobile phone number and sms code sent by
      * AV.User.requestLoginSmsCode.On success, this

test/user.js

@@ -30,23 +30,33 @@ describe("User",function(){
 
 });
 
-describe("UserSignin",function(){
+describe("User.logIn and User.become",function(){
   it("should login",function(done){
     AV.User.logIn(username, password, {
       success: function(user) {
         expect(user.get("username")).to.be(username);
-        done();
+        console.dir(user);
+        AV.User.become(user._sessionToken, {
+            success: function(theUser) {
+                expect(theUser.get("username")).to.be(username);
+                done();
+            },
+            error: function(err){
+                throw err;
+            }
+        });
         // Do stuff after successful login.
       },
       error: function(user, error) {
-        throw eror;
+        throw error;
         // The login failed. Check error to see why.
       }
     });
 
   });
 });
 
+
 describe("Current User",function(){
   it("should return current user",function(done){