In environments with SAML authentication, if required Claim fields aren't entered on IDP side for user account, then login will be redirected to a Page Not Found on Gallery.
Alteryx Server with SAML Authentication
Version: 2023.1, 2022.3
Reviewing the AAS logs located in %PROGRAMDATA%\Alteryx\Logs\ identifies an issue with a null value in one of the Required Claims fields (FirstName, LastName, Email).
INFO,52,AlteryxServerWebApiHost,ssoLogger,Acs,,,,,,,,,,"Unauthorized since firstName: test_alteryx, lastName: and email: test_alteryx@test.com cannot be null in the SAML response since 'FirstName', 'LastName' and 'Email' are required to create a session."
1. Contact your identity provider (IdP) to ensure that none of the three required claim fields (FirstName, LastName, Email) are null.
2. Once all required claim fields are populated, test by logging in to Gallery.
If this does not resolve the issue, please see this article with a different root cause for this error: 403 Forbidden/Page Not Found after login to Gallery when using SAML authentication.