How to Verify Azure Access Tokens for Microsoft Graph API at the Backend

Learn how to effectively verify Azure access tokens for Microsoft Graph API calls in your backend. Explore the solution to acquiring access tokens securely and properly handling token verification.
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How to Verify Azure Access Tokens for Microsoft Graph API at the Backend

Are you struggling with verifying Azure access tokens for Microsoft Graph API in your backend? This is a common scenario developers face when working with token-based authentication. Understanding how to acquire and verify these tokens correctly can streamline your application's security and functionality. In this post, we'll break down the issue and provide a clear solution.

The Problem

When you use Azure AD to obtain an access token on your frontend for the Microsoft Graph API, you naturally want to ensure that this token is valid and secure when sent to your backend. The questions you might have include:

How do I verify the access token at the backend?

What steps do I need to ensure the token is valid?

Are there any common mistakes to avoid in this process?

Understanding Access Tokens

An access token is a JWT (JSON Web Token) that your frontend app receives after authentication with Azure. This token is used to authorize calls to Microsoft Graph API. However, verifying this token at your backend can have its intricacies:

Token Purpose: Access tokens are usually scoped to specific APIs. In scenarios where a token is generated for Microsoft Graph, it’s not necessarily meant for your backend API. This is key to understanding why you may face verification issues.

A Clear Solution

To resolve the token verification issue, it is crucial to follow the correct flow when dealing with tokens. Here are the steps to ensure you handle token verification effectively:

Step 1: Acquire Access Token for Your API

Instead of verifying the token meant for Microsoft Graph API at your backend, you should have your frontend request an access token specifically for your backend API. This is important because:

Microsoft Graph tokens are issued for Graph API alone and are not intended for your backend API verification.

A dedicated token for your API simplifies verification.

Step 2: Verify the Token for Your API

After obtaining the access token for your backend API, you can verify it using standard JWT verification methods. Here's a simplified flow:

Use a JWT library (like jsonwebtoken in Node.js) to validate the token.

Check the token's signature and ensure it corresponds with the key you have set up for your API.

Step 3: On-Behalf-Of Flow

To call Microsoft Graph API securely after verifying your API token, utilize the On-Behalf-Of (OBO) flow:

After validating the access token for your API, you can request a new token for the Microsoft Graph API using the OBO flow. This allows you to exchange your valid API token for a Graph API token.

Example Code Snippet for Validating Your API Token

Here's how you might go about verifying the token for your backend API using Node.js:

[[See Video to Reveal this Text or Code Snippet]]

Final Thoughts

Verifying access tokens does not need to be a daunting task. By ensuring that you request and verify tokens intended for your API, and integrating the On-Behalf-Of flow, you can maintain a secure and efficient authentication process.

If you were stuck with the verification of Microsoft Graph API tokens, remember that those are meant solely for Microsoft Graph itself. Shift your focus on validating the token for your API, and you'll set yourself on the right path.



By following the steps outlined above, you can clearly address token verification in your backend, ensuring a secure interaction with Azure and Microsoft Graph API. Happy coding!