freeradius with NTLM authentication

I have configured freeradius version 2.1.9 with mySQL backend and Active Directory integration (NTLM) for the purpose of using it to authenticate users against firewall protected policies. So far it’s all working. When a user hits a firewall protected policy he is prompted to authenticate after which the radius query the AD for the username and password. If the user credentials are correct access is granted. The bit that I cannot figure out is how to let the Radius use NTLM to check if the user is already logged in the domain controller and if so not to prompt him for his username and password via the firewall captive portal. Is that doable or I missed the idea behind the Active Directory integration? thank you Ramzi