Dual Factor Authentication with LDAP (Active Directory)

Dears,

I have my LDAP servers configured and also FSSO configured I can see the groups and I can use my AD users in security policies everything works perfect, My company wants a dual factor authentication for SSL vpn users 1st authentication with AD and the other with RSA token, I have added the RSA token server as a radius server but how I can route authentication first to AD and then a hop from AD to  RSA token , I am confused how I can setup dual factor authentication when AD is configured with FSSO.

Can anybody help me with similar setup and configuration example.

thanks