Hello @Jessica, Tandazo {GC} ,
Thank you for reaching out Microsoft Q&A.
I Understand that you have an issue with attributes from users in Azure portal for an Enterprise application named Secure Connect, you want the attribute mapping in the application to take the value: On-premises user principal name, but you cannot find this attribute in the mapping options because the user attributes supported for a given application are preconfigured.
Most application's user management APIs don't support schema discovery. So, the Microsoft Entra provisioning service isn't able to dynamically generate the list of supported attributes by making calls to the application.
For additional information follow: https://learn.microsoft.com/en-us/entra/identity/app-provisioning/customize-application-attributes
Hope this helps. Do let us know if you any further queries.
Regards,
Goutam Pratti.