How to Resolve Modern Authentication (ADAL/MSAL) Failures in 2025

Modern Authentication failures in Microsoft 365 occur when desktop applications fail to exchange OAuth tokens through the Microsoft Authentication Library (MSAL) or deprecated Active Directory Authentication Library (ADAL). This failure causes sign-in windows to disappear, blank authentication pop-ups to freeze, or repeated credential prompts in Outlook, Teams, and Word. It stops desktop apps from connecting to Exchange Online and SharePoint, even when login credentials are correct. Restoring sign-in functionality requires clearing legacy ADAL registry overrides and resetting the Windows Web Account Manager (WAM) broker.

Fast-Fix: The 45-Second Solution

Modern authentication failures stem from legacy ADAL registry overrides or corrupted Web Account Manager (WAM) token caches following Microsoft’s shift to MSAL protocols. Risk Tier: Moderate. Fix this by deleting legacy EnableADAL registry keys, re-registering the Microsoft.AAD.BrokerPlugin package in PowerShell, and clearing cached identity credentials before restarting your client applications.

Diagnostic Snapshot

• Severity Tier: Moderate (Blocks desktop app login and cloud sync; web versions remain functional).
• Data Safety Risk: Low (Local document files and cloud mailboxes remain completely safe).
• Common Cause: Legacy registry keys overriding MSAL, corrupted WAM identity cache, or stale OAuth tokens.
• Admin Requirement: User permissions for standard sign-outs; Local Administrator rights for registry and PowerShell repairs.

Condition: Low Risk vs. High Risk

• Low Risk: The authentication prompt freezes or fails on a single computer after a Windows update, while web browser access to Microsoft 365 works fine.
• High Risk: Sign-in fails across all Office applications for multiple users on domain-joined devices, accompanied by Conditional Access block warnings or device compliance errors in Entra ID.

The System Break (What This Means)

Microsoft 365 uses Modern Authentication built on OAuth 2.0 protocols. In older Office builds, authentication was handled by ADAL, which created embedded browser windows inside each application to request passwords. Modern Windows 10 and 11 environments use MSAL, which hands off login handling to the operating system’s Web Account Manager (Microsoft.AAD.BrokerPlugin).

Think of ADAL as a store issuing its own paper claim tickets at every counter, while MSAL is a central digital wristband issued at the front door. If an old registry rule tells Outlook to demand a paper ticket (ADAL) while the cloud server only accepts the digital wristband (MSAL), the sign-in exchange stalls. The app sits waiting for a response that never arrives, producing blank dialog windows or endless login loops.

Root Cause Probability

• Likely (60%): Legacy registry keys (EnableADAL or DisableAADWAM) forcing deprecated authentication flows on modern builds.
• Possible (30%): Corrupted OAuth refresh tokens or identity caches in %LocalAppData%\Microsoft\IdentityCache and Windows Credential Manager.
• Rare (10%): WebView2 runtime corruption preventing the Windows login interface from rendering properly.

Conflict Escalators

• Upgraded Systems: Computers upgraded from older Office versions often retain stale registry keys under HKCU\Software\Microsoft\Office\16.0\Common\Identity that force legacy ADAL protocols.
• Third-Party Antivirus & Web Proxies: Endpoint security tools that inspect SSL traffic can interfere with background token exchanges to login.microsoftonline.com.
• Hybrid Join Conflicts: Switching between corporate domain credentials and personal Microsoft accounts can cause WAM to assign the wrong tenant ID during silent token refreshes.

Progression: 1 Hour -> 24 Hours -> 1 Week

• 1 Hour: Outlook displays a yellow “Need Password” or “Disconnected” notification at the bottom of the window, and clicking it produces no response or a blank box.
• 24 Hours: Cached access tokens expire completely. Word, Excel, and Teams enter read-only mode or sign out entirely.
• 1 Week: Unresolved authentication failures prevent background license checks, placing desktop apps into Reduced Functionality Mode.

Common Misdiagnoses

• Misdiagnosed as an Invalid Password: Users frequently re-type passwords or reset account credentials. However, if the login window won’t render or loops endlessly, the password isn’t the problem, the token transport layer is.
• Misdiagnosed as a Hardware TPM Error: While TPM issues cause authentication failures, TPM errors usually generate explicit error codes like 80090016. If your issue involves hardware chip storage, see Troubleshooting TPM 2.0 Errors (80090016) during Office Sign-in.
• Misdiagnosed as General Account Disablement: If you can log into portal.office.com using Edge or Chrome, your tenant account is healthy. Do not attempt account resets; focus on local OS authentication components.

Immediate Action Steps

Step 1: Remove Legacy ADAL and WAM Registry Overrides

Legacy registry keys meant for older Office builds break MSAL authentication flows on modern installations. Removing them allows Windows to use standard MSAL handing.

1. Press Windows Key + R, type regedit, and press Enter.
2. Navigate to: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity
3. Look for the following DWORD entries in the right pane:
   • EnableADAL
   • DisableAADWAM
   • DisableADALatWorkaDay
4. If present, right-click each entry and select Delete.
   (Note: Setting EnableADAL to 0 or DisableAADWAM to 1 disables modern broker authentication. Deleting them restores default MSAL behavior.)
5. Restart your computer.

Step 2: Clear Cached Identity Tokens

Remove stale authentication tokens from the local user profile to force a clean login session.

1. Close all Microsoft 365 applications.
2. Press Windows Key + R, type %LocalAppData%\Microsoft and press Enter.
3. Locate the IdentityCache folder, right-click it, and select Delete.
4. Press Windows Key + R, type control keymgr.dll and press Enter to open Credential Manager.
5. Select Windows Credentials and delete all saved entries starting with MicrosoftOffice16_Data or ADAL.
6. For detailed steps on removing stale credentials safely, refer to How to Clear Stale Office Tokens from Windows Credential Manager.

Step 3: Re-register the Windows Web Account Manager (WAM)

If sign-in boxes remain blank, re-registering the WAM broker package fixes corrupted system files handling MSAL prompts.

1. Right-click the Start menu and select PowerShell (Admin) or Terminal (Admin).
2. Run the following command: PowerShell Add-AppxPackage -Register "C:\Windows\SystemApps\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy\AppxManifest.xml" -DisableDevelopmentMode -ForceApplicationShutdown
3. If WAM cache corruption persists, follow the advanced broker reset steps detailed in Resolving “Something Went Wrong” Error 1001 in Outlook and Teams.

Step 4: Reset the Microsoft 365 Activation State

If clearing registry overrides and credentials does not restore sign-in prompts, reset the activation layer using automated tools as outlined in How to Reset the Microsoft 365 Activation State (Using SaRA Tool).

Hard-Stop Red Flags

• “Access Denied by Conditional Access”: If sign-in fails with explicit policy codes like CA20001, your authentication token is valid, but your device or network location violates company security rules. See Troubleshooting “CA20001” Conditional Access Sign-in Errors.
• Missing SystemApps Directory: If the PowerShell command returns a “Path Not Found” error for Microsoft.AAD.BrokerPlugin, the Windows operating system image is damaged and requires a DISM or SFC system repair.

What the IT Admin Will Check

1. Entra ID Sign-in Logs: Check the Entra ID portal for failed authentication logs under the user’s account to identify whether failures stem from blocked legacy authentication protocols.
2. Group Policy & Intune Policies: Verify that no Administrative Templates (GPO) are deploying legacy EnableADAL registry keys across managed endpoints.
3. WebView2 Runtime Health: Ensure the Microsoft Edge WebView2 Evergreen Runtime is installed and updated, as MSAL relies on WebView2 to render modern sign-in prompts.

Resolution Complexity

• Moderate: Requires modifying user registry entries, clearing system folders, and running elevated PowerShell commands.

Related Error Escalators

• If authentication succeeds but credentials are requested every time you reboot Windows, review How to Clear Office Credential Cache on Windows 11 (The Modern Way).
• If sign-in windows load but fail due to network connection timeouts, see Office Activation Fails with “Server Not Responding”.

Ticket Closed

Modern Authentication failures in 2025 are almost always caused by legacy registry keys blocking MSAL or a corrupted WAM token cache. Removing obsolete EnableADAL or DisableAADWAM registry values and re-registering the Microsoft.AAD.BrokerPlugin package restores standard sign-in pop-ups. Once these steps are completed and the system is rebooted, open any Office app to log in normally.