How to Fix Legacy Office Add-In Authentication with Microsoft Entra ID

When organizations migrate their identity management to the cloud, older desktop extensions often break. If you are working to Fix Legacy Office Add-In Authentication with Microsoft Entra ID, you are likely dealing with continuous password prompts, blocked access errors, or freezing interfaces when interacting with older COM or VSTO add-ins. This occurs because Microsoft Entra ID (formerly Azure AD) enforces Modern Authentication and multi-factor authentication (MFA) by default, while legacy add-ins often rely on deprecated protocols like Basic Authentication or the outdated Active Directory Authentication Library (ADAL). Resolving this requires updating how the local Office client handles identity tokens, adjusting application permissions in your tenant, or identifying security policies blocking the connection.

Enabling Modern Authentication to Add-Ins via Windows Registry

The most common and immediately actionable method for fixing Legacy Office Add-In Authentication with Microsoft Entra ID is forcing the Office client to route all authentication requests through the Web Account Manager (WAM). Older add-ins sometimes attempt to use legacy browser controls or bypass WAM, causing silent authentication failures.

You can enforce WAM and Modern Authentication using the Windows Registry Editor. Follow these explicit steps:

• Press Win + R, type regedit, and press Enter to open the Registry Editor.
• Navigate to the following exact path: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity.
• Right-click the Identity folder, select New > DWORD (32-bit) Value, and name it EnableADAL. Double-click it and set the Value data to 1.
• Create another DWORD (32-bit) Value named DisableADALatopWAMOverride and set its Value data to 0.
• Create a third DWORD (32-bit) Value named DisableAADWAM and set its Value data to 0.

After creating these keys, close the Registry Editor and restart your computer. Launch the Office application (such as Excel or Word) and click the legacy add-in button. The expected result is a native Microsoft Entra ID pop-up window prompting for credentials, rather than a blank screen or a legacy basic authentication dialog.

Configuring Application Registrations in Microsoft Entra ID

If the local registry fix does not resolve the issue, the add-in might be communicating with a backend service that lacks proper authorization in your cloud environment. while working on fixing Legacy Office Add-In Authentication with Microsoft Entra ID from an administrative perspective, you must verify the App Registration settings.

Legacy add-ins often require admin consent for specific API permissions or rely on public client flows. To verify and adjust these settings:

• Log in to the Microsoft Entra admin center (entra.microsoft.com) using a Global Administrator or Cloud Application Administrator account.
• Expand the Applications menu on the left sidebar and click App registrations.
• Click the All applications tab and search for the name or Client ID of your specific legacy add-in.
• Select the application and click API permissions from the left-hand navigation menu.
• Check the Status column. If any permission shows a warning, click the Grant admin consent for [Your Tenant Name] button above the permissions list and confirm the prompt.
• Next, click Authentication in the left menu. Scroll down to the Advanced settings section.
• Locate the Allow public client flows toggle and set it to Yes. Click Save at the top of the page.

Instruct the affected user to sign out of their Office application and sign back in. Trigger the add-in again. The verification step is successful when the Entra ID sign-in logs show a successful token issuance for that specific application ID.

Reviewing Conditional Access Policies for Legacy Blocks

Another crucial step in fixing Legacy Office Add-In Authentication with Microsoft Entra ID involves your organization's security policies. Microsoft Entra ID Conditional Access policies are frequently configured to block legacy authentication entirely. If your add-in relies on older protocols like POP, IMAP, or direct credential passing, Entra ID will drop the connection.

To diagnose and temporarily bypass this for troubleshooting:

• In the Microsoft Entra admin center, navigate to Protection > Conditional Access.
• Click on Sign-in logs in the monitoring section. Filter the logs by the affected user and look for entries with a Failure status.
• Click the failed log entry and navigate to the Conditional Access tab in the details pane. Identify the specific policy causing the block (often named "Block Legacy Authentication").
• Return to Protection > Conditional Access > Policies and open the blocking policy.
• Under the Assignments section, click Users, switch to the Exclude tab, and add your test user account. Click Save.

Wait approximately 15 minutes for the policy change to propagate. Have the user attempt to authenticate via the add-in again. If successful, you have confirmed legacy authentication is the root cause. Note that leaving legacy authentication enabled is a severe security risk; this step should only be used to diagnose the issue before pushing the add-in vendor for a modern update.

Updating from ADAL to MSAL

If you have access to the add-in's source code, the permanent method for fixing Legacy Office Add-In Authentication with Microsoft Entra ID is migrating the authentication library. The Active Directory Authentication Library (ADAL) reached end-of-life and is no longer supported by Microsoft Entra ID. Developers must migrate the codebase to the Microsoft Authentication Library (MSAL).

Open your project in Visual Studio. Open the NuGet Package Manager and uninstall the Microsoft.IdentityModel.Clients.ActiveDirectory package. Search for and install Microsoft.Identity.Client. You must rewrite the authentication logic to replace the `AuthenticationContext` class with the `PublicClientApplicationBuilder` class. Compile the updated add-in, deploy it to a test machine, and verify that the authentication flow correctly utilizes the system's default browser or WAM for modern token acquisition.

Handling Document Workflows with WPS Office

Addressing fixing Legacy Office Add-In Authentication with Microsoft Entra ID is strictly a Microsoft ecosystem administration task. WPS Office cannot change Microsoft Entra ID tenant settings, modify Microsoft Conditional Access policies, or force Microsoft Office to authenticate legacy COM add-ins.

However, if your organization relies on a broken legacy add-in simply to generate standard document templates, merge data, or extract text, you may not need to rely on that failing architecture at all. WPS Office provides an independent, lightweight office suite that handles complex document workflows natively. If your underlying goal is document generation rather than software troubleshooting, you can open your standard DOCX or XLSX files directly in WPS Writer or WPS Spreadsheet. For modern workflows, you can utilize WPS Office's integrated AI assistant to auto-generate document structures, summarize data, or extract text from PDFs without requiring third-party legacy extensions. To do this, open WPS Office, create a new document, and click the WPS AI button on the Home ribbon to input your prompt or data parameters, effectively bypassing the need for the broken legacy add-in entirely.

Use Word, Excel, and PPT for FREE

Free Download

Frequently Asked Questions

Why does the add-in prompt for a password repeatedly after migrating to Entra ID?

Repeated password prompts usually indicate a token caching failure or an inability to interface with the Web Account Manager (WAM). The add-in is successfully authenticating but failing to store or retrieve the refresh token from the Windows credentials manager. Enforcing WAM through the registry keys detailed above usually resolves this caching loop.

Can I bypass multi-factor authentication (MFA) for a specific legacy Office add-in?

While you can exclude a specific user or application from MFA via Conditional Access policies in the Microsoft Entra admin center, this is highly discouraged for security reasons. If the add-in cannot handle MFA prompts, the secure alternative is to update the application to support MSAL, which handles MFA natively via interactive browser pop-ups.

How do I check if my installed add-in uses the deprecated ADAL framework?

You can inspect the installation directory of the add-in on your local hard drive. Navigate to the folder where the add-in is installed (often in Program Files or AppData). Look for a file named Microsoft.IdentityModel.Clients.ActiveDirectory.dll. If this DLL file is present in the directory, the add-in relies on the deprecated ADAL framework and requires an update from the developer.

Will enabling "Allow public client flows" compromise my tenant security?

Enabling public client flows in an App Registration allows the application to use older, less secure authentication methods like Resource Owner Password Credentials (ROPC), which transmits usernames and passwords directly. This bypasses modern security controls and MFA. You should only enable this setting as a temporary bridge for legacy add-ins while actively working on migrating the application to a modern OAuth 2.0 authorization code flow.