AppAuth-iOS: An Objective-C repository from matadan

AppAuth for iOS and macOS is a client SDK for communicating with OAuth 2.0 and OpenID Connect providers. It strives to directly map the requests and responses of those specifications, while following the idiomatic style of the implementation language. In addition to mapping the raw protocol flows, convenience methods are available to assist with common tasks like performing an action with fresh tokens.

It follows the best practices set out in RFC 8252 - OAuth 2.0 for Native Apps including using SFAuthenticationSession and SFSafariViewController on iOS for the auth request. UIWebView and WKWebView are explicitly not supported due to the security and usability reasons explained in Section 8.12 of RFC 8252.

It also supports the PKCE extension to OAuth which was created to secure authorization codes in public clients when custom URI scheme redirects are used. The library is friendly to other extensions (standard or otherwise) with the ability to handle additional params in all protocol requests and responses.

Specification

iOS

Supported Versions

AppAuth supports iOS 7 and above.

iOS 9+ uses the in-app browser tab pattern (via SFSafariViewController), and falls back to the system browser (mobile Safari) on earlier versions.

Authorization Server Requirements

Both Custom URI Schemes (all supported versions of iOS) and Universal Links (iOS 9+) can be used with the library.

In general, AppAuth can work with any Authorization Server (AS) that supports native apps as documented in RFC 8252, either through custom URI scheme redirects, or universal links. AS's that assume all clients are web-based or require clients to maintain confidentiality of the client secrets may not work well.

macOS

Supported Versions

AppAuth supports macOS (OS X) 10.9 and above.

Authorization Server Requirements

AppAuth for macOS supports both custom schemes, a loopback HTTP redirects via a small embedded server.

In general, AppAuth can work with any Authorization Server (AS) that supports native apps as documented in RFC 8252, either through custom URI scheme, or loopback HTTP redirects. AS's that assume all clients are web-based or require clients to maintain confidentiality of the client secrets may not work well.

Try

Want to try out AppAuth? Just run:

pod try AppAuth

Follow the instructions in Examples/README.md to configure with your own OAuth client (you need to update 3 configuration points with your client info to try the demo).

Setup

AppAuth supports three options for dependency management.

CocoaPods

With CocoaPods, add the following line to your Podfile:

pod 'AppAuth'

Then run pod install.

Carthage

With Carthage, add the following line to your Cartfile:

github "openid/AppAuth-iOS" "master"

Then run carthage bootstrap.

Static Library

You can also use AppAuth as a static library. This requires linking the library and your project and including the headers. Suggested configuration:

Create an Xcode Workspace.
Add AppAuth.xcodeproj to your Workspace.
Include libAppAuth as a linked library for your target (in the "General -> Linked Framework and Libraries" section of your target).
Add AppAuth-iOS/Source to your search paths of your target ("Build Settings -> "Header Search Paths").

Auth Flow

AppAuth supports both manual interaction with the Authorization Server where you need to perform your own token exchanges, as well as convenience methods that perform some of this logic for you. This example uses the convenience method which returns either an OIDAuthState object, or an error.

OIDAuthState is a class that keeps track of the authorization and token requests and responses, and provides a convenience method to call an API with fresh tokens. This is the only object that you need to serialize to retain the authorization state of the session.

Configuration

You can configure AppAuth by specifying the endpoints directly:

NSURL *authorizationEndpoint =
    [NSURL URLWithString:@"https://accounts.google.com/o/oauth2/v2/auth"];
NSURL *tokenEndpoint =
    [NSURL URLWithString:@"https://www.googleapis.com/oauth2/v4/token"];

OIDServiceConfiguration *configuration =
    [[OIDServiceConfiguration alloc]
        initWithAuthorizationEndpoint:authorizationEndpoint
                        tokenEndpoint:tokenEndpoint];

// perform the auth request...

Or through discovery:

NSURL *issuer = [NSURL URLWithString:@"https://accounts.google.com"];

[OIDAuthorizationService discoverServiceConfigurationForIssuer:issuer
    completion:^(OIDServiceConfiguration *_Nullable configuration,
                 NSError *_Nullable error) {

  if (!configuration) {
    NSLog(@"Error retrieving discovery document: %@",
          [error localizedDescription]);
    return;
  }

  // perform the auth request...
}];

Authorizing – iOS

First you need to have a property in your AppDelegate to hold the session, in order to continue the authorization flow from the redirect.

// property of the app's AppDelegate
@property(nonatomic, strong, nullable)
    id<OIDExternalUserAgentSession> currentAuthorizationFlow;

And your main class, a property to store the auth state:

// property of the containing class
@property(nonatomic, strong, nullable) OIDAuthState *authState;

Then, initiate the authorization request. By using the authStateByPresentingAuthorizationRequest convenience method, the token exchange will be performed automatically, and everything will be protected with PKCE (if the server supports it). AppAuth also allows you to perform these requests manually. See the authNoCodeExchange method in the included Example app for a demonstration.

// builds authentication request
OIDAuthorizationRequest *request =
    [[OIDAuthorizationRequest alloc] initWithConfiguration:configuration
                                                  clientId:kClientID
                                                    scopes:@[OIDScopeOpenID,
                                                             OIDScopeProfile]
                                               redirectURL:kRedirectURI
                                              responseType:OIDResponseTypeCode
                                      additionalParameters:nil];

// performs authentication request
AppDelegate *appDelegate =
    (AppDelegate *)[UIApplication sharedApplication].delegate;
appDelegate.currentAuthorizationFlow =
    [OIDAuthState authStateByPresentingAuthorizationRequest:request
        presentingViewController:self
                        callback:^(OIDAuthState *_Nullable authState,
                                   NSError *_Nullable error) {
  if (authState) {
    NSLog(@"Got authorization tokens. Access token: %@",
          authState.lastTokenResponse.accessToken);
    [self setAuthState:authState];
  } else {
    NSLog(@"Authorization error: %@", [error localizedDescription]);
    [self setAuthState:nil];
  }
}];

Handling the Redirect

The authorization response URL is returned to the app via the iOS openURL app delegate method, so you need to pipe this through to the current authorization session (created in the previous session).

- (BOOL)application:(UIApplication *)app
            openURL:(NSURL *)url
            options:(NSDictionary<NSString *, id> *)options {
  // Sends the URL to the current authorization flow (if any) which will
  // process it if it relates to an authorization response.
  if ([_currentAuthorizationFlow resumeExternalUserAgentFlowWithURL:url]) {
    _currentAuthorizationFlow = nil;
    return YES;
  }

  // Your additional URL handling (if any) goes here.

  return NO;
}

Authorizing – MacOS

On macOS, the most popular way to get the authorization response redirect is to start a local HTTP server on the loopback interface (limited to incoming requests from the user's machine only). When the authorization is complete, the user is redirected to that local server, and the authorization response can be processed by the app. AppAuth takes care of managing the local HTTP server lifecycle for you.

💡 Alternative: Custom URI Schemes

Custom URI schemes are also supported on macOS, but some browsers display an interstitial which reduces the usability. For an example on using custom URI schemes with macOS, See Example-Mac.

To receive the authorization response using a local HTTP server, first you need to have an instance variable in your main class to retain the HTTP redirect handler.

OIDRedirectHTTPHandler *_redirectHTTPHandler;

Then, as the port used by the local HTTP server varies, you need to start it before building the authorization request in order to get the exact redirect URI to use.

static NSString *const kSuccessURLString =
    @"http://openid.github.io/AppAuth-iOS/redirect/";
NSURL *successURL = [NSURL URLWithString:kSuccessURLString];

// Starts a loopback HTTP redirect listener to receive the code.  This needs to be started first,
// as the exact redirect URI (including port) must be passed in the authorization request.
_redirectHTTPHandler = [[OIDRedirectHTTPHandler alloc] initWithSuccessURL:successURL];
NSURL *redirectURI = [_redirectHTTPHandler startHTTPListener:nil];

Then, initiate the authorization request. By using the authStateByPresentingAuthorizationRequest convenience method, the token exchange will be performed automatically, and everything will be protected with PKCE (if the server supports it). By assigning the return value to the OIDRedirectHTTPHandler's currentAuthorizationFlow, the authorization will continue automatically once the user makes their choice.

// builds authentication request
OIDAuthorizationRequest *request =
    [[OIDAuthorizationRequest alloc] initWithConfiguration:configuration
                                                  clientId:kClientID
                                              clientSecret:kClientSecret
                                                    scopes:@[ OIDScopeOpenID ]
                                               redirectURL:redirectURI
                                              responseType:OIDResponseTypeCode
                                      additionalParameters:nil];
// performs authentication request
__weak __typeof(self) weakSelf = self;
_redirectHTTPHandler.currentAuthorizationFlow =
    [OIDAuthState authStateByPresentingAuthorizationRequest:request
                        callback:^(OIDAuthState *_Nullable authState,
                                   NSError *_Nullable error) {
  // Brings this app to the foreground.
  [[NSRunningApplication currentApplication]
      activateWithOptions:(NSApplicationActivateAllWindows |
                           NSApplicationActivateIgnoringOtherApps)];

  // Processes the authorization response.
  if (authState) {
    NSLog(@"Got authorization tokens. Access token: %@",
          authState.lastTokenResponse.accessToken);
  } else {
    NSLog(@"Authorization error: %@", error.localizedDescription);
  }
  [weakSelf setAuthState:authState];
}];

Making API Calls

AppAuth gives you the raw token information, if you need it. However we recommend that users of the OIDAuthState convenience wrapper use the provided performActionWithFreshTokens: method to perform their API calls to avoid needing to worry about token freshness.

[_authState performActionWithFreshTokens:^(NSString *_Nonnull accessToken,
                                           NSString *_Nonnull idToken,
                                           NSError *_Nullable error) {
  if (error) {
    NSLog(@"Error fetching fresh tokens: %@", [error localizedDescription]);
    return;
  }

  // perform your API request using the tokens
}];

API Documentation

Browse the API documentation.

Included Samples

Sample apps that explore core AppAuth features are available for iOS and macOS, follow the instructions in Examples/README.md to get started.

matadan/AppAuth-iOS

Specification

iOS

Supported Versions

Authorization Server Requirements

macOS

Supported Versions

Authorization Server Requirements

Try

Setup

CocoaPods

Carthage

Static Library

Auth Flow

Configuration

Authorizing – iOS

Authorizing – MacOS

💡 Alternative: Custom URI Schemes

Making API Calls

API Documentation

Included Samples