Do you mean you want the IP of the browser where the server call was initiated? Sadly an anvil.http.request to ip.jsontest.com will give you one of our egress IPs where the outgoing request actually originates.
We don’t currently have a mechanism for getting client information from the current session, but it’s on our (very) long list of features that would be nice to have. Customers on our Anvil support plans are able to commission or prioritise features on our roadmap - please do get in touch by email if that is something you would be interested in.
EDIT: You can now get the client IP from anvil.server.context