Step by Step Guide to Building an Azure Active Directory API Integration in C#

Introduction

Hey there, fellow developer! Ready to dive into the world of Azure Active Directory (Azure AD) integration? You're in the right place. We'll be using the Microsoft.Identity.Client package to make our lives easier. Let's get cracking!

Prerequisites

Before we jump in, make sure you've got:

• Visual Studio (any recent version will do)
• .NET 5.0 or later
• An Azure AD tenant (if you don't have one, no worries – it's free to set up)

Setting up the project

First things first:

1. Fire up Visual Studio and create a new C# project.
2. Install the Microsoft.Identity.Client NuGet package. In the Package Manager Console, run:

Install-Package Microsoft.Identity.Client

Configuring Azure AD

Head over to the Azure portal and register your application. Jot down the Client ID and Tenant ID – you'll need these later.

Implementing authentication

Now for the fun part! Let's authenticate:

using Microsoft.Identity.Client;

var app = PublicClientApplicationBuilder
    .Create(clientId)
    .WithAuthority(AzureCloudInstance.AzurePublic, tenantId)
    .WithRedirectUri("http://localhost")
    .Build();

string[] scopes = { "user.read" };

AuthenticationResult result;
try
{
    result = await app.AcquireTokenSilent(scopes, account).ExecuteAsync();
}
catch (MsalUiRequiredException)
{
    result = await app.AcquireTokenInteractive(scopes).ExecuteAsync();
}

Making API calls

Got your token? Great! Let's use it:

using var client = new HttpClient();
client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", result.AccessToken);
var response = await client.GetAsync("https://graph.microsoft.com/v1.0/me");

Handling token caching

Don't make your users log in every time! Implement token caching:

app.UserTokenCache.SetBeforeAccess(notificationArgs =>
{
    // Load your cache from secure storage
});

app.UserTokenCache.SetAfterAccess(notificationArgs =>
{
    // Save your cache to secure storage
});

Error handling and token refresh

Always be prepared for the unexpected:

try
{
    // Your API call here
}
catch (MsalUiRequiredException)
{
    // Token expired, refresh it
    result = await app.AcquireTokenInteractive(scopes).ExecuteAsync();
}

Best practices

• Keep your secrets secret! Use Azure Key Vault or similar for storing sensitive info.
• Implement proper error handling and logging.
• Use async/await consistently for better performance.

Testing and debugging

Use Azure AD test tenants for development. When debugging, set breakpoints in your authentication flow to understand what's happening under the hood.

Conclusion

And there you have it! You've just built an Azure AD integration in C#. Pretty cool, right? Remember, this is just the tip of the iceberg. There's so much more you can do with Azure AD and Microsoft.Identity.Client.

Keep exploring, keep coding, and most importantly, have fun! If you get stuck, the Microsoft docs are your best friend. Happy coding!