What is MSAL?

The Microsoft Authentication Library (MSAL) enables applications to authenticate users using a variety of Microsoft identities. It allows applications to leverage the Microsoft identity platform, supporting authentication with Microsoft accounts, Azure AD accounts, and accounts from other identity providers that are integrated with Azure AD.

Key Features

• Support for Multiple Platforms: MSAL offers libraries for many platforms including .NET, JavaScript, Python, and others.
• Integration with Microsoft Identity Platform: MSAL seamlessly integrates with Microsoft’s identity services, enabling secure sign-in and authorization for users.
• Token Acquisition and Management: It simplifies the process of acquiring tokens for accessing Microsoft APIs and managing them effectively.

MSAL vs. ADAL

MSAL is the successor to the Azure Active Directory Authentication Library (ADAL). While ADAL only supports work and school accounts, MSAL extends its support to personal Microsoft accounts, as well as social and local accounts using Azure AD B2C (Business to Consumer).

Comparison Between ADAL and MSAL

Why Use MSAL?

• Future-Proof: Microsoft recommends MSAL for all new applications and advises migrating from ADAL to MSAL for existing applications, as ADAL will no longer receive new feature updates.
• Broader Identity Options: MSAL’s support for a wider range of identities makes it a more flexible choice for diverse user bases.
• Enhanced Security: It aligns with modern security practices, including support for OAuth 2.0 and OpenID Connect standards.

Scenarios for Using MSAL

• Single Sign-On (SSO): MSAL enables SSO across multiple applications, improving the user experience by reducing the number of sign-ins required.
• Accessing Microsoft Graph: Applications that require access to Microsoft Graph can use MSAL to authenticate users and acquire tokens.
• Multi-platform Applications: For applications that span across various platforms, MSAL provides a consistent authentication experience.

Implementing MSAL

To implement MSAL in your application, you first need to register your application with the Microsoft identity platform. This registration process involves creating an application ID and configuring authentication parameters.

Steps for Registration

1. Azure Portal: Navigate to the Azure portal and access the Azure Active Directory service.
2. App Registration: Go to “App registrations” and create a new registration.
3. Set Redirect URIs: Specify the redirect URIs, which are the endpoints where users will be redirected after authentication.
4. Obtain Application (Client) ID: Once registered, note down the Application (Client) ID. This ID will be used in your application code to initialize MSAL.

Integrating MSAL in Your Application

The integration process varies depending on the platform and language you are using. Here’s a general outline for a .NET application:

• Install MSAL Library

Install-Package Microsoft.Identity.Client

• Initialise MSAL

var clientBuilder = PublicClientApplicationBuilder.Create(clientId)
  .WithRedirectUri(redirectUri)
  .Build();

• Acquire Tokens

AuthenticationResult result = 
  await clientBuilder.AcquireTokenInteractive(scopes).ExecuteAsync();

Handling Token Lifecycle

MSAL handles the token lifecycle, including refreshing tokens when they are about to expire. It caches tokens and provides them for subsequent requests without needing to re-authenticate the user.

Token Refresh Process

• Silent Token Acquisition: Before making an API call, try to acquire a token silently.
• Token Refresh: If the token is expired, MSAL automatically requests a new token using the refresh token.
• Token Caching: MSAL caches the tokens and manages their lifecycle, reducing the need to manually handle token storage and refresh.

Error Handling

When implementing MSAL, handle errors such as failed authentication or token acquisition. MSAL provides detailed error information that can be used to inform users or take corrective actions.

Common Error Scenarios

• User Cancelation: The user cancels the sign-in process.
• Network Issues: Issues with network connectivity leading to authentication failures.
• Invalid Scope: Requested scopes are not configured or are invalid.

Best Practices

• Scope Management: Request only the necessary scopes required for your application.
• Secure Storage: Ensure that the token cache is stored securely, especially in public client applications.
• Logging and Monitoring: Implement logging and monitoring for the authentication process to troubleshoot and improve the authentication flow.

Best Practices for Using MSAL

1. Understand the OAuth2 and OpenID Connect Flows: Before implementing MSAL, it’s essential to have a good understanding of the OAuth2 and OpenID Connect protocols. This knowledge helps in correctly implementing authentication and authorization flows.
2. Use the Latest MSAL Libraries: Always use the latest version of MSAL libraries. Microsoft continuously updates these libraries with new features, security improvements, and bug fixes.
3. Minimize Scope Requests: Request only the permissions that are absolutely necessary for your application. Over-requesting permissions can lead to security risks and might deter users from using your app.
4. Handle Token Renewal Gracefully: MSAL handles token renewal, but ensure your application handles scenarios where the renewal might fail, such as when the user’s credentials have changed or the user is offline.
5. Secure the Token Cache: In applications where a token cache is used, secure it properly to prevent unauthorized access to tokens.
6. Implement Robust Error Handling: Proper error handling in your application can improve the user experience significantly, especially in scenarios like network failures or authentication errors.
7. Monitor and Log Authentication Flows: Keeping logs and monitoring the authentication processes can help in diagnosing issues and understanding user behavior.

Common Scenarios

1. Web Application Sign-In: Implementing sign-in for web applications using MSAL to authenticate users with Microsoft identities.
2. Single Page Applications (SPA): Using MSAL.js in SPAs to handle authentication with interactive and silent token requests.
3. Desktop and Mobile Applications: Integrating MSAL in desktop and mobile applications for secure user authentication and token acquisition.
4. API Access with MSAL: Acquiring tokens to access Microsoft Graph or other APIs securely. This involves getting the right scopes and handling token acquisition and refresh.
5. Conditional Access and Multi-Factor Authentication (MFA): Implementing conditional access policies and handling MFA challenges within applications.
6. B2B and B2C Scenarios: Using MSAL in applications that cater to business-to-business (B2B) or business-to-consumer (B2C) scenarios, accommodating a variety of identity types.
7. Integrating with Legacy Systems: Transitioning from ADAL to MSAL in systems that were previously using older authentication libraries.

Conclusion

Implementing MSAL requires understanding the basic flow of registering the application, initializing the library, acquiring tokens, and handling their lifecycle. By following these steps and best practices, developers can effectively integrate Microsoft identity capabilities into their applications

Further information on MSAL can be found on Microsoft’s site here: https://learn.microsoft.com/en-us/entra/identity-platform/msal-overview