Hi,
I assume you are using FlexVPN. You will need to use aaa authorization, name-mangler to distinguish between users in the different vrf's, multiple loopback interfaces on the router in the different vrfs and use "ip address negoiated" under the tunnel interface. Once authorized the correct loopback will be assigned to the VA interface and the AC user will be able to access resources in that vrf.
Here is an example, it's for a S2S VPN but the same principal applies. It uses ISE as a RADIUS server for authorization, you could use another RADIUS server - the av-pairs required are listed.
HTH