Storefront logout and re-authenticate with no prompt for credentials

Hi, We've integrated citrix storefront with F5 (11.6.2) recently by using iApp . Everything works great but we have an issue with the authentication to the storefront once user logs off from the citrix, Users are able to logon without prompting for username and password when clicked on logon. We are using Imprivata for Radius and its MFA. Any help would be much appreciated.

FYI: no user sessions should be terminated after logout is enabled.