enforce radius username with AD username in vmware view client

Currently we have iApp built using vmware view client with Radius and the APM webpage is working fine as it asks all the details in one screen but the VMware View Client is not enforcing the radius username captured in first screen to the Windows AD credentials screen asked in the second screen after radius authentication.

We looked at the flow and couldn't find any place to enforce the session.logon.last.username in the windows AD username field. We also want to configure this field as readonly to restrict users changing the username value that was enforced from the radius login screen.

This is a configurable in VMware connection server directly (ref: https://pubs.vmware.com/view-52/index.jsp?topic=%2Fcom.vmware.view.administration.doc%2FGUID-71458AA2-E2A2-43AC-85D1-35404AF09B79.html) but as we want to use F5 as connection broker with iApp, we couldn't find this setting on BIG-IP iApp.

Thanks in advance!