title: AFOAuth2Client unable to access resource
body: <p>Using AFOAuth2Client and AFNetworking on iOS 6 I am able to get an access token, but am unable to access a resource, the server responds with a status code of 401 unauthorized. This is against a custom Rails 3 API backend using doorkeeper as the OAuth provider. The following client ruby code, using the OAuth2 gem, works OK:</p>
  
  <pre><code>client = OAuth2::Client.new(app_id, secret, site: "http://subdomain.example.com/")
  access_token = client.password.get_token('username', 'password')
  access_token.get('/api/1/products').parsed
  </code></pre>
  
  <p>The iOS code is as below, in the login button handler I authenticate using the username and password, and store the credentials:</p>
  
  <pre><code>- (IBAction)login:(id)sender {
      NSString *username = [usernameField text];
      NSString *password = [passwordField text];
  
      NSURL *url = [NSURL URLWithString:kClientBaseURL];
      AFOAuth2Client *client = [AFOAuth2Client clientWithBaseURL:url clientID:kClientID secret:kClientSecret];
  
      [client authenticateUsingOAuthWithPath:@"oauth/token"
                                username:username
                                password:password
                                   scope:nil
                                 success:^(AFOAuthCredential *credential) {
                                     NSLog(@"Successfully received OAuth credentials %@", credential.accessToken);
                                     [AFOAuthCredential storeCredential:credential
                                                         withIdentifier:client.serviceProviderIdentifier];
                                     [self performSegueWithIdentifier:@"LoginSegue" sender:sender];
                                 }
                                 failure:^(NSError *error) {
                                     NSLog(@"Error: %@", error);
                                     [passwordField setText:@""];
                                 }];
  }
  </code></pre>
  
  <p>and I've subclassed <code>AFHTTPClient</code> for my endpoint and in <code>initWithBaseURL</code> it retrieves the credentials and sets the authorization header with the access token:</p>
  
  <pre><code>- (id)initWithBaseURL:(NSURL *)url {
      self = [super initWithBaseURL:url];
      if (!self) {
          return nil;
      }
  
      [self registerHTTPOperationClass:[AFJSONRequestOperation class]];
      [self setDefaultHeader:@"Accept" value:@"application/json"];
  
      AFOAuthCredential *credential = [AFOAuthCredential retrieveCredentialWithIdentifier:@"subdomain.example.com"];
      [self setAuthorizationHeaderWithToken:credential.accessToken];
  
      return self;
  }
  </code></pre>
  
  <p>Is this the correct way to use AFOAuth2Client and AFNetworking? And any idea why this is not working?</p>