HTTP Header: X-Insta-Forwarded-For
Value: [IP information]|[Signature]
IP information: Comma-separated list of one or more IPs; if your app receives requests directly from clients, then it should be the client's remote IP as detected by the your app's load balancer; if your app is behind another load balancer (for example, Amazon's ELB), this should contain the exact contents of the original X-Forwarded-For header. You can use the 127.0.0.1 loopback address during testing.
Signature: Using your Client Secret, apply an HMAC with SHA256, and append the hex representation of the signature there.