[CRD iOS] Implementing save to keychain and user defaults for login info. Refactor remoting service.

remoting/client/ios/facade/remoting_authentication.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef REMOTING_CLIENT_IOS_FACADE_REMOTING_AUTHENTICATION_H_
+#define REMOTING_CLIENT_IOS_FACADE_REMOTING_AUTHENTICATION_H_
+
+#import "remoting/client/chromoting_client_runtime.h"
+#import "remoting/client/ios/domain/user_info.h"
+
+#include "base/memory/weak_ptr.h"
+#include "remoting/base/oauth_token_getter.h"
+
+// |RemotingAuthenticationDelegate|s are interested in authentication related
+// notifications.
+@protocol RemotingAuthenticationDelegate<NSObject>
+
+// Notifies the delegate that the user has been updated.
+- (void)userDidUpdate:(UserInfo*)user;
+
+@end
+
+// This is the class that will manage the details around authentication
+// management and currently active user. It will make sure the user object is
+// saved to the keychain correctly and loaded on startup. It also is the entry
+// point for gaining access to an auth token for authrized calls.
+@interface RemotingAuthentication : NSObject
+
+// Provide an |authorizationCode| to authenticate a user as the first time user
+// of the application or OAuth Flow.
+- (void)authenticateWithAuthorizationCode:(NSString*)authorizationCode;
+
+// Provide the |refreshToken| and |email| to authenticate a user as a returning
+// user of the application.
+- (void)authenticateWithRefreshToken:(NSString*)refreshToken
+                               email:(NSString*)email;
+
+// Fetches an OAuth Access Token and passes it back to the callback.
+- (void)callbackWithAccessToken:

[Yuwei, 2017/05/04 05:10:14]

This method doesn't really fetch the OAuth token if none of authenticateWith*
has been called. Fix this comment and maybe also fix the method name?

[nicholss, 2017/05/08 17:08:10]

I think the method name is ok, I added a comment. But in time I think it will
need to be 
refactored to add an error code as well. Added a TODO for that.

+    (const remoting::OAuthTokenGetter::TokenCallback&)onAccessToken;
+
+// Forget the current user.
+- (void)logout;
+
+// Returns the currently logged in user or nil.
+@property(strong, nonatomic) UserInfo* user;
+
+// Delegate recieves updates on user changes.
+@property(weak, nonatomic) id<RemotingAuthenticationDelegate> delegate;
+
+@end
+
+#endif  // REMOTING_CLIENT_IOS_FACADE_REMOTING_AUTHENTICATION_H_