Malicious clients and proxies can provide potentially malicious strings
in the polls. This validates the NAT type and proxy type strings to
ensure that malformed strings are not displayed on a web page
or passed to any of our monitoring infrastructure.
If a client or proxy supplies an invalid NAT type, we return an error
message. If a proxy supplies an unknown proxy type, we set the proxy
type to unknown.
Send the client poll request and response in a json-encoded format in
the HTTP request body rather than sending the data in HTTP headers. This
will pave the way for using domain-fronting alternatives for the
Snowflake rendezvous.
