AFOAuth2Client is an extension for AFNetworking that greatly simplifies the process of authenticating against an OAuth 2 provider.
NSURL *url = [NSURL URLWithString:@"http://example.com/"];
AFOAuth2Client *oauthClient = [AFOAuth2Client clientWithBaseURL:url clientID:kClientID secret:kClientSecret];
[oauthClient authenticateUsingOAuthWithPath:@"/oauth/token"
                                   username:@"username"
                                   password:@"password"
                                      scope:@"email"
                                    success:^(AFOAuthCredential *credential) {
                                        NSLog(@"I have a token! %@", credential.accessToken);
                                        [AFOAuthCredential storeCredential:credential withIdentifier:oauthClient.serviceProviderIdentifier];
                                    }
                                    failure:^(NSError *error) {
                                        NSLog(@"Error: %@", error);
                                    }];Mattt Thompson
AFOAuth2Client is available under the MIT license. See the LICENSE file for more info.