Enable authentication in your own iOS Swift app by using Azure AD B2C

Grein
01/11/2024

This article shows you how to add Azure Active Directory B2C (Azure AD B2C) authentication to your own iOS Swift mobile application. Learn how to integrate an iOS Swift application with the Microsoft Authentication Library (MSAL) for iOS.

Use this article with Configure authentication in a sample iOS Swift application, substituting the sample iOS Swift app with your own iOS Swift app. After you've completed the instructions in this article, your application will accept sign-ins via Azure AD B2C.

Prerequisites

Review the prerequisites and integration instructions in Configure authentication in a sample iOS Swift app by using Azure AD B2C.

Create an iOS Swift app project

If you don't already have an iOS Swift application, set up a new project by doing the following steps:

Open Xcode, and then select File > New > Project.
For iOS apps, select iOS > App, and then select Next.
For Choose options for your new project, provide the following:
1. Product name, such as MSALiOS.
2. Organization identifier, such as contoso.com.
3. For the Interface, select Storyboard.
4. For the Life cycle, select UIKit App Delegate.
5. For the Language, select Swift.
Select Next.
Select a folder in which to create your app, and then select Create.

Step 1: Install the MSAL library

Use CocoaPods to install the MSAL library. In the same folder as your project's .xcodeproj file, if the podfile file doesn't exist, create an empty file and name it podfile. Add the following code to the podfile file:
```
use_frameworks!

target '<your-target-here>' do
   pod 'MSAL'
end
```
Replace <your-target-here> with the name of your project (for example, MSALiOS). For more information, see Podfile Syntax Reference.
In a terminal window, go to the folder that contains the podfile file, and then run pod install to install the MSAL library.
After you run the pod install command, a <your project name>.xcworkspace file is created. To reload the project in Xcode, close Xcode, and then open the <your project name>.xcworkspace file.

Step 2: Set the app URL scheme

When users authenticate, Azure AD B2C sends an authorization code to the app by using the redirect URI configured on the Azure AD B2C application registration.

The MSAL default redirect URI format is msauth.[Your_Bundle_Id]://auth. An example would be msauth.com.microsoft.identitysample.MSALiOS://auth, where msauth.com.microsoft.identitysample.MSALiOS is the URL scheme.

In this step, register your URL scheme by using the CFBundleURLSchemes array. Your application listens on the URL scheme for the callback from Azure AD B2C.

In Xcode, open the Info.plist file as a source code file. In the <dict> section, add the following XML snippet:

<key>CFBundleURLTypes</key>
<array>
    <dict>
        <key>CFBundleURLSchemes</key>
        <array>
            <string>msauth.com.microsoft.identitysample.MSALiOS</string>
        </array>
    </dict>
</array>
<key>LSApplicationQueriesSchemes</key>
<array>
    <string>msauthv2</string>
    <string>msauthv3</string>
</array>

Step 3: Add the authentication code

The sample code is made up of a UIViewController class. The class:

Defines the structure for a user interface.
Contains information about your Azure AD B2C identity provider. The app uses this information to establish a trust relationship with Azure AD B2C.
Contains the authentication code to authenticate users, acquire tokens, and validate them.

Choose a UIViewController where users authenticate. In your UIViewController, merge the code with the code that's provided in GitHub.

Step 4: Configure your iOS Swift app

After you add the authentication code, configure your iOS Swift app with your Azure AD B2C settings. Azure AD B2C identity provider settings are configured in the UIViewController class that was chosen in the previous section.

To learn how to configure your iOS Swift app, see Configure authentication in a sample iOS Swift app by using Azure AD B2C.

Step 5: Run and test the mobile app

Build and run the project with a simulator of a connected iOS device.
Select Sign In, and then sign up or sign in with your Azure AD B2C local or social account.
After you've authenticated successfully, you'll see your display name in the navigation bar.

Step 6: Customize your code building blocks

This section describes the code building blocks that enable authentication for your iOS Swift app. It lists the UIViewController's methods and discusses how to customize your code.

Step 6.1: Instantiate a public client application

Public client applications aren't trusted to safely keep application secrets, and they don't have client secrets. In viewDidLoad, instantiate an MSAL by using a public client application object.

The following Swift code snippet demonstrates how to initialize the MSAL with a MSALPublicClientApplicationConfig configuration object.

The configuration object provides information about your Azure AD B2C environment. For example, it provides the client ID, redirect URI, and authority to build authentication requests to Azure AD B2C. For information about the configuration object, see Configure the sample mobile app.

do {

    let signinPolicyAuthority = try self.getAuthority(forPolicy: self.kSignupOrSigninPolicy)
    let editProfileAuthority = try self.getAuthority(forPolicy: self.kEditProfilePolicy)
    
    let pcaConfig = MSALPublicClientApplicationConfig(clientId: kClientID, redirectUri: kRedirectUri, authority: signinPolicyAuthority)
    pcaConfig.knownAuthorities = [signinPolicyAuthority, editProfileAuthority]
    
    self.applicationContext = try MSALPublicClientApplication(configuration: pcaConfig)
    self.initWebViewParams()
    
    } catch {
        self.updateLoggingText(text: "Unable to create application \(error)")
    }

The initWebViewParams method configures the interactive authentication experience.

The following Swift code snippet initializes the webViewParameters class member with the system web view. For more information, see Customize browsers and WebViews for iOS/macOS.

func initWebViewParams() {
    self.webViewParameters = MSALWebviewParameters(authPresentationViewController: self)
    self.webViewParameters?.webviewType = .default
}

Step 6.2: Start an interactive authorization request

An interactive authorization request is a flow where users are prompted to sign up or sign in by using the system web view. When users select the Sign In button, the authorizationButton method is called.

The authorizationButton method prepares the MSALInteractiveTokenParameters object with relevant data about the authorization request. The acquireToken method uses the MSALInteractiveTokenParameters to authenticate users via the system web view.

The following code snippet demonstrates how to start the interactive authorization request:

let parameters = MSALInteractiveTokenParameters(scopes: kScopes, webviewParameters: self.webViewParameters!)
parameters.promptType = .selectAccount
parameters.authority = authority

applicationContext.acquireToken(with: parameters) { (result, error) in

// On error code    
guard let result = result else {
    self.updateLoggingText(text: "Could not acquire token: \(error ?? "No error information" as! Error)")
    return
}

// On success code
self.accessToken = result.accessToken
self.updateLoggingText(text: "Access token is \(self.accessToken ?? "Empty")")
}

After users finish the authorization flow, either successfully or unsuccessfully, the result is returned to the closure of the acquireToken method.

The acquireToken method returns the result and error objects. Use this closure to:

Update the mobile app UI with information after the authentication is completed.
Call a web API service with an access token.
Handle authentication errors (for example, when a user cancels the sign-in flow).

Step 6.3: Call a web API

To call a token-based authorization web API, the app needs a valid access token. The app does the following:

Acquires an access token with the required permissions (scopes) for the web API endpoint.
Passes the access token as a bearer token in the authorization header of the HTTP request by using this format:

Authorization: Bearer <access-token>

When users authenticate interactively, the app gets an access token in the acquireToken closure. For subsequent web API calls, use the acquire token silent (acquireTokenSilent) method, as described in this section.

The acquireTokenSilent method does the following actions:

It attempts to fetch an access token with the requested scopes from the token cache. If the token is present and hasn't expired, the token is returned.
If the token isn't present in the token cache or it has expired, the MSAL library attempts to use the refresh token to acquire a new access token.
If the refresh token doesn't exist or has expired, an exception is returned. In this case, you should prompt the user to sign in interactively.

The following code snippet demonstrates how to acquire an access token:

do {

// Get the authority using the sign-in or sign-up user flow
let authority = try self.getAuthority(forPolicy: self.kSignupOrSigninPolicy)

// Get the current account from the application context
guard let thisAccount = try self.getAccountByPolicy(withAccounts: applicationContext.allAccounts(), policy: kSignupOrSigninPolicy) else {
    self.updateLoggingText(text: "There is no account available!")
    return
}

// Configure the acquire token silent parameters
let parameters = MSALSilentTokenParameters(scopes: kScopes, account:thisAccount)
parameters.authority = authority
parameters.loginHint = "username"

// Acquire token silent
self.applicationContext.acquireTokenSilent(with: parameters) { (result, error) in
    if let error = error {
        
        let nsError = error as NSError
        
        // interactionRequired means we need to ask the user to sign in. This usually happens
        // when the user's Refresh Token is expired or if the user has changed their password
        // among other possible reasons.
        
        if (nsError.domain == MSALErrorDomain) {
            
            if (nsError.code == MSALError.interactionRequired.rawValue) {
                
                // Start an interactive authorization code
                // Notice we supply the account here. This ensures we acquire token for the same account
                // as we originally authenticated.
                
                ...
            }
        }
        
        self.updateLoggingText(text: "Could not acquire token: \(error)")
        return
    }
    
    guard let result = result else {
        
        self.updateLoggingText(text: "Could not acquire token: No result returned")
        return
    }
    
    // On success, set the access token to the accessToken class member. 
    // The callGraphAPI method uses the access token to call a web API  
    self.accessToken = result.accessToken
    ...
}
} catch {
self.updateLoggingText(text: "Unable to construct parameters before calling acquire token \(error)")
}

The callGraphAPI method retrieves the access token and calls the web API, as shown here:

@objc func callGraphAPI(_ sender: UIButton) {
    guard let accessToken = self.accessToken else {
        self.updateLoggingText(text: "Operation failed because could not find an access token!")
        return
    }
    
    let sessionConfig = URLSessionConfiguration.default
    sessionConfig.timeoutIntervalForRequest = 30
    let url = URL(string: self.kGraphURI)
    var request = URLRequest(url: url!)
    request.setValue("Bearer \(accessToken)", forHTTPHeaderField: "Authorization")
    let urlSession = URLSession(configuration: sessionConfig, delegate: self, delegateQueue: OperationQueue.main)
    
    self.updateLoggingText(text: "Calling the API....")
    
    urlSession.dataTask(with: request) { data, response, error in
        guard let validData = data else {
            self.updateLoggingText(text: "Could not call API: \(error ?? "No error information" as! Error)")
            return
        }
        
        let result = try? JSONSerialization.jsonObject(with: validData, options: [])
        
        guard let validResult = result as? [String: Any] else {
            self.updateLoggingText(text: "Nothing returned from API")
            return
        }
        
        self.updateLoggingText(text: "API response: \(validResult.debugDescription)")
        }.resume()
}

Step 6.4: Sign out users

Signing out with MSAL removes all known information about users from the application. Use the sign-out method to sign out users and update the UI. For example, you can hide protected UI elements, hide the sign-out button, or show the sign-in button.

The following code snippet demonstrates how to sign out users:

@objc func signoutButton(_ sender: UIButton) {
do {
    
    
    let thisAccount = try self.getAccountByPolicy(withAccounts: applicationContext.allAccounts(), policy: kSignupOrSigninPolicy)
    
    if let accountToRemove = thisAccount {
        try applicationContext.remove(accountToRemove)
    } else {
        self.updateLoggingText(text: "There is no account to signing out!")
    }
    
    ...
    
} catch  {
    self.updateLoggingText(text: "Received error signing out: \(error)")
}
}

Next steps

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