Environment Details
- Alteryx Server with Windows Authentication
Users trying to access the Gallery for the first time will receive the below error message:

An unknown error occurred during authentication with your Windows credentials.
Cause
To understand the root cause of this issue, we will need to search for additional error messages.
- In the Gallery Logs:
-
INFO,94,AuthorizationMessageInspector,BeforeSendReply,9d0a8e84095248db8f007e0032fc10aa,unauthenticated,172.23.202.31,ALTERYXGALLERY,"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.79 Safari/537.36 Edge/14.14393",POST,/gallery/api/auth/sessions/,400,161,CloudResponse,
...
ERROR,53,ErrorHandler,HandleError,,,,,,,,,,Exception caught by ErrorHandler and marshalled to client,"Alteryx.Cloud.Common.Exceptions.BadRequestException: The specified email address does not meet our email format standards.
- The POST request to /gallery/api/auth/sessions/ returns a 400 error
- This is followed by a "BadRequestException: The specified email address does not meet our email format standards".
- In the Browser's devtools:

- it displays the same 400 error for the /gallery/api/auth/sessions/ endpoint with the same error message
This means that the email address returned by querying the Active Directory doesn't comply to the requirements of Alteryx Server.
Resolution
Here we requested the IT to display the user properties as saved under Active Directory:

We found out that there is a space in between the @ and the domain in the email
E-mail field.
In other cases, this field would even appear as empty.
The next and final step is to ask IT to fix it so the access to Gallery is functional again.