Copilot OAuth Implicit Flow Deprecated Warning: Migration Steps

You may see a warning in your Microsoft Entra admin center that the OAuth 2.0 implicit grant flow is deprecated for Copilot integrations. This affects apps that authenticate users or acquire tokens for Copilot using the implicit flow, which Microsoft has marked as deprecated. The implicit flow is less secure than the authorization code flow with PKCE. This article explains why the deprecation matters and provides step-by-step migration steps for your application.

Why Microsoft Deprecated the OAuth Implicit Flow for Copilot

The OAuth 2.0 implicit grant flow was originally designed for browser-based single-page applications. In this flow, the access token is returned directly in the URL fragment after user authentication. This exposes the token in the browser history, server logs, and referrer headers, creating a security risk. An attacker who gains access to the browser or network logs can capture the token and use it to access Copilot APIs on behalf of the user.

Microsoft deprecated the implicit flow in 2023 and began enforcing the deprecation in early 2025. Any application that still uses the implicit flow to authenticate against Microsoft Entra ID for Copilot will see a deprecation warning in the admin center. The warning appears in the App registrations blade under Authentication, next to the implicit grant settings.

The recommended replacement is the authorization code flow with PKCE. PKCE stands for Proof Key for Code Exchange. It adds a dynamically generated secret to the authorization request. This prevents interception attacks even if the authorization code is intercepted. The authorization code flow never exposes the access token in the URL, making it significantly more secure.

Steps to Migrate Copilot Integrations from Implicit Flow to Authorization Code Flow

The migration involves two main areas: updating the app registration in the Microsoft Entra admin center and modifying the application code. Follow these steps in order.

Step 1: Update App Registration in Microsoft Entra Admin Center

1. Sign in to Microsoft Entra admin center
   Go to https://entra.microsoft.com and sign in with a Global Administrator or Application Administrator account.
2. Open App registrations
   In the left navigation, select Applications > App registrations. Find the app that uses the implicit flow for Copilot.
3. Navigate to Authentication settings
   Click the app name, then select Authentication from the left menu.
4. Disable implicit grant
   Under Implicit grant and hybrid flows, uncheck both Access tokens and ID tokens. Click Save.
5. Add a redirect URI for authorization code flow
   Under Redirect URIs, add a URI that uses https and points to your application. For a single-page app, use a URI like https://yourdomain.com/auth/callback. For a native app, use https://login.microsoftonline.com/common/oauth2/nativeclient. Click Configure.
6. Enable PKCE support
   Microsoft Entra ID supports PKCE by default for public clients. No additional checkbox is needed. Ensure your app registration is set as a Public client/native under Authentication > Advanced settings if it is a desktop or mobile app.

Step 2: Modify Application Code to Use Authorization Code Flow with PKCE

1. Install the latest Microsoft Authentication Library
   Use MSAL.js version 2.x or later for browser apps. For .NET, use MSAL.NET 4.30 or later. For Python, use MSAL Python 1.15 or later. These libraries support PKCE by default.
2. Replace the implicit flow call with authorization code call
   In your code, remove the response_type: 'token' or response_type: 'id_token token' parameter. Use response_type: 'code' instead. Example in MSAL.js:
   const msalConfig = { auth: { clientId: 'your-client-id', authority: 'https://login.microsoftonline.com/your-tenant-id', redirectUri: 'https://yourdomain.com/auth/callback' } };
const loginRequest = { scopes: ['openid', 'profile', 'User.Read', 'https://graph.microsoft.com/.default'] };
const msalInstance = new PublicClientApplication(msalConfig);
const response = await msalInstance.loginPopup(loginRequest); The library handles PKCE automatically.
3. Exchange the authorization code for tokens
   After the redirect back to your app, MSAL exchanges the authorization code for an access token. You do not need to manually call the token endpoint. The library does this behind the scenes.
4. Acquire tokens silently for Copilot API calls
   Use acquireTokenSilent to get tokens without user interaction. Example:
   const tokenRequest = { scopes: ['https://graph.microsoft.com/.default'], account: msalInstance.getAllAccounts()[0] };
const tokenResponse = await msalInstance.acquireTokenSilent(tokenRequest);
   Use tokenResponse.accessToken in the Authorization header of your Copilot API requests.
5. Test the new flow
   Sign out of your app, then sign in again. Verify that no implicit grant warning appears in the Entra admin center. Check that Copilot API calls return data successfully.

If Migration to Authorization Code Flow Fails

Copilot API returns 401 Unauthorized after migration

The access token might be missing the correct scopes. In the token request, include the scope https://graph.microsoft.com/.default to get a token for all Microsoft Graph permissions your app needs. If your app uses Copilot-specific scopes, add them explicitly, for example https://graph.microsoft.com/Copilot.Read.

Redirect URI mismatch error

The redirect URI in the app registration must exactly match the URI in your code, including the trailing slash. Check for extra spaces or different casing. For local development, use http://localhost:3000/auth/callback but note that production URIs must use https.

PKCE error: code_challenge_method not supported

MSAL libraries version 2.x and later automatically use S256 as the code challenge method. If you are using a custom OAuth library, ensure you set code_challenge_method=S256 and generate the code verifier and code challenge correctly. The code verifier must be a random string of 43 to 128 characters using unreserved characters.

Implicit Flow vs Authorization Code Flow with PKCE: Key Differences

Item	Implicit Flow	Authorization Code Flow with PKCE
Token exposure	Access token returned in URL fragment	Access token returned in server-side HTTP response
Security risk	High — token visible in browser history and logs	Low — token never appears in URL
PKCE support	Not supported	Built-in with S256 challenge method
Refresh token	Not issued	Issued for long-lived sessions
Microsoft recommendation	Deprecated	Recommended for all app types

After you complete the migration, verify that no deprecation warning appears in the Microsoft Entra admin center under your app registration. The warning disappears once the implicit grant settings are disabled and the app uses the authorization code flow. Monitor your Copilot API usage for a few days to confirm tokens are acquired and refreshed without errors. For advanced scenarios, consider adding token cache persistence to avoid repeated sign-in prompts.