Add session validation

[bneradt]

@SolidWallOfCode has mentioned that it would be helpful if Proxy Verifier had the ability to verify certain properties of the session. He mentioned specifically wanting to verify the ip address of the session. Here are other possible properties to validate:

• Validate the ip protocol (v4 or v6)
• Validate the HTTP protocol (HTTP/1 or HTTP/2)
• Validate whether the connection is secured via HTTPS.

This would be server side session validation since the client itself connects according to its own parameters. Currently, verifier-server does no session validation against the way the proxy connects to it. This issue records the desire to be able to do such validation against the way the proxy connects to verifier-server.

[bneradt]

#29 gets us closer to this because it adds support for server-side protocol configuration on every proxy-request. On top of that, we would want to add verification to satisfy this issue.