IPSEC over BGP using Fortinet 6.0

One of our clients uses 2 VPNs over BGP on 2 Cisco ASA. We use a Fortigate VM64 version 6.0.4 running on AWS. We need to know how to establish a IPSEC connection with our Fortigate to the client. Would this look like a normal ipsec site to site vpn or are there special factors I need to keep in mind. I cannot be sure but I assume the client is running iBGP to connect their own ASes.   I would appreciate any help from forum members. Thank you very much.