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Problem - Exchange 2019 CU15 & Modern Auth through on-prem ADFS

Romain 0 Reputation points
2025-08-05T05:27:36.2966667+00:00

Hi,

I am trying to configure Modern Auth with my up-to-date Exchange 2019 CU15 DAG.  Please note that I want to authenticate through my on-prem ADFS and not Office 365.  Outlook version is Microsoft® Outlook® for Microsoft 365 MSO (Version 2506 Build 16.0.18925.20076) 64-bit. 

I followed this tutorial: https://learn.microsoft.com/en-us/exchange/plan-and-deploy/post-installation-tasks/enable-modern-auth-in-exchange-server-on-premises#how-will-modern-authentication-work-and-is-this-feature-applicable-to-me  However, I am unable to get Outlook client to work with it.

More info:  On client side, I added the few registry keys in the tutorial + others I found during my research: 

HKEY_CURRENT_USER\SOFTWARE\Microsoft\office\16.0\outlook\autodiscover  DWORD: ExcludeExplicitO365Endpoit

HKEY_CURRENT_USER\Software\Microsoft\Exchange\  DWORD: AlwaysUseMSOAuthForAutoDiscover 

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\15.0\Common\Identity\  DWORD: EnableADAL 

 

When I launch Outlook, the ADFS authentication window appears as expected.  I enter my credentials, but then it spins indefinitely.  If I add my account to a new profile, the same thing happens, except that I end up with error 62ubh (An error occurred).

 Looking at the ADFS side, authentication works fine. There is no error log about it.  If I run Fiddler on my computer, I can see that ADFS is sending me a valid token. 

My Outlook calls https://adfs.myfakedomain.com/adfs/oauth2/authorize then https://adfs.myfakedomain.com/adfs/oauth2/token, but once the token is received, a new URL is called and ends with 404 error:  https://adfs.myfakedomain.com/common/sso/progress?stage=Closing 

I can't debug any further and understand what's happening.  I don't know if it's the return URL sent by ADFS that's incorrect, or if it's my Outlook that doesn't understand the response from my ADFS and wants to close the SSO session.  I don't understand why it doesn't move on to step 7 of the process (schema on the howto from Microsoft).   

Based on my understanding, Outlook should now contact my Exchanges with the newly received tokens, right? 

I would therefore appreciate your help in clarifying this for me.

Exchange | Exchange Server | Other
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  1. Vergil-V 2,115 Reputation points Microsoft External Staff Moderator
    2025-08-05T08:50:41.2966667+00:00

    Hi Romain 
    Thank you for reaching out to Microsoft Learn Q&A!  Based on your description, I understand you're encountering a 404 error when the URL …/common/sso/progress?stage=Closing is called, along with an error code 62ubh after ADFS authentication in Outlook. 

    As a forum moderator, I want to acknowledge that we do not have access to a dedicated testing environment to replicate user-specific scenarios. However, driven by our mission to support users within the scope of our capabilities, I’d like to share some troubleshooting steps that may help you investigate further or provide more context around the issue: 

    +Verify Registry Keys 
    Please double-check that the three relevant registry keys are set to a value of 1, which ensures the feature is enabled. 

    +Review ADFS Relying Party Trust (RPT) 
    Ensure that the Relying Party Trust (RPT) includes the correct endpoints, valid claims rules (such as UPN and email), and a valid token-signing certificate. You can use the Get-AdfsRelyingPartyTrust command to review these settings. For more details, please refer to Get-AdfsRelyingPartyTrust (ADFS) | Microsoft Learn. 

    +Use Event Viewer 
    Check logs in Event Viewer to gather more information and identify any underlying issues. 

    +Restart Services 
    Restarting IIS and ADFS services is a general troubleshooting step that may help resolve temporary issues. 

    As mentioned, due to platform limitations, I’m unable to provide an exact solution without additional context. Your feedback is incredibly valuable and helps us improve the support we offer. If you have any updates or further questions, please don’t hesitate to reach out. 

    If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".         

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