[CRD iOS] Refactor an interface for RemotingAuthorization

remoting/ios/app/client_connection_view_controller.mm

Index: remoting/ios/app/client_connection_view_controller.mm
diff --git a/remoting/ios/app/client_connection_view_controller.mm b/remoting/ios/app/client_connection_view_controller.mm
index 5ccc95486ab132d18c1677dd207e334081c9bd2e..888ee2c358ea998c6de2cf1d4f89f90508397ad5 100644
--- a/remoting/ios/app/client_connection_view_controller.mm
+++ b/remoting/ios/app/client_connection_view_controller.mm
@@ -60,15 +60,13 @@ static const CGFloat kKeyboardAnimationTime = 0.3;
     _client = [[RemotingClient alloc] init];
 
     __weak RemotingClient* weakClient = _client;
-    [[RemotingService SharedInstance].authentication
-        callbackWithAccessToken:base::BindBlockArc(^(
-                                    remoting::OAuthTokenGetter::Status status,
-                                    const std::string& user_email,
-                                    const std::string& access_token) {
+    [RemotingService.instance.authentication
+        callbackWithAccessToken:^(RemotingAuthenticationStatus status,
+                                  NSString* userEmail, NSString* accessToken) {
           [weakClient connectToHost:hostInfo
-                           username:base::SysUTF8ToNSString(user_email)
-                        accessToken:base::SysUTF8ToNSString(access_token)];
-        })];
+                           username:userEmail
+                        accessToken:accessToken];
+        }];
 
     _remoteHostName = hostInfo.hostName;