Fix X-Matrix signature validation for incoming requests
For HTTP/1 requests, an inbound Request's URI contains only the path and query parameters, since there's no way to synthesize the authority part. This is exactly what we need for the X-Matrix "uri" field.
HTTP/2 requests however can contain the :authority pseudo-header, which is used to populate the Request's URI. Using a URL that includes an authority breaks the signature check.
Largely inspired by conduit MR !631.