freeswitch to authenticate just with ip address

Hi I need a hand with freeswitch:

I have a client that needs to send calls to my freeswitch
but his switch doesn't have username+password authentication.

He is asking me to have my freeswitch accept the calls based on his public ip address.

Let me know if you are able to help
but only bid if you have extensive experience with freeswitch
as this is a security concern.

Max 100 euros.


Thank you.