AFOAuth2Client and refresh token

How to implement the Oauth in iPad application?

How does AFOAuth2Client manages refreshing token mechanism in oauth 2.0?

Is there any method to implement it inside the class or do we have to implement it in our own way? How to check the token is expired or not?

The way that I have solved this is to wrap all my requests with a code block which will refresh the access token if needed e.g.

Add some typedefs for success and failure blocks:

typedef void (^YFRailsSaasApiClientSuccess)(AFJSONRequestOperation *operation, id responseObject);
typedef void (^YFRailsSaasApiClientFailure)(AFJSONRequestOperation *operation, NSError *error);

Then the request method is:

- (void)getProductsWithSuccess:(YFRailsSaasApiClientSuccess)success failure:(YFRailsSaasApiClientFailure)failure {
    NSLog(@"getProductsWithSuccess");

    success = ^(AFJSONRequestOperation *operation, id responseObject) {
        [self getPath:@"api/1/products"
           parameters:nil
              success:^(AFHTTPRequestOperation *operation, id responseObject) {
                  NSLog(@"getProductsWithSuccess: success");

                  // TODO: handle response

                  if (success) {
                      success((AFJSONRequestOperation *)operation, responseObject);
                  }
              } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                  NSLog(@"getProductsWithSuccess: failure");
              if (failure) {
                  failure((AFJSONRequestOperation *)operation, error);
              }
          }];
    };

    [self refreshAccessTokenWithSuccess:success failure:failure];
}

And the method which checks for token expiry and refreshes it if needed is:

- (void)refreshAccessTokenWithSuccess:(YFRailsSaasApiClientSuccess)success failure:(YFRailsSaasApiClientFailure)failure {
    NSLog(@"refreshAccessTokenWithSuccess");

    if (self.credential == nil) {
        if (failure) {
            NSMutableDictionary *errorDetail = [NSMutableDictionary dictionary];
            [errorDetail setValue:@"Failed to get credentials" forKey:NSLocalizedDescriptionKey];
            NSError *error = [NSError errorWithDomain:@"world" code:200 userInfo:errorDetail];
            failure(nil, error);
        }
        return;
    }  

    if (!self.credential.isExpired) {
        NSLog(@"refreshAccessTokenWithSuccess: credential has not expired");

        if (success) {
            success(nil, nil);
        }
        return;
    }

    NSLog(@"refreshAccessTokenWithSuccess: refreshing credential");

    [self authenticateUsingOAuthWithPath:@"oauth/token"
                            refreshToken:self.credential.refreshToken
                                 success:^(AFOAuthCredential *newCredential) {
                                     NSLog(@"Successfully refreshed OAuth credentials %@", newCredential.accessToken);
                                     self.credential = newCredential;
                                     [AFOAuthCredential storeCredential:newCredential
                                                     withIdentifier:self.serviceProviderIdentifier];

                                     if (success) {
                                         success(nil, nil);
                                     }
                                 }
                                 failure:^(NSError *error) {
                                     NSLog(@"An error occurred refreshing credential: %@", error);
                                     if (failure) {
                                         failure(nil, error);
                                     }
                                 }];
}

Full source code is up on GitHub: https://github.com/yellowfeather/rails-saas-ios.