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Glossary

HTTP CONNECT

The HTTP method that asks a proxy to open a raw tunnel, which is how HTTPS travels through an HTTP proxy.

CONNECT asks a proxy to establish a TCP tunnel to a destination and then relay bytes without interpreting them. It is the mechanism that lets encrypted HTTPS traffic pass through a proxy that otherwise speaks HTTP.

#The exchange

CONNECT api.example.com:443 HTTP/1.1
Host: api.example.com:443
Proxy-Authorization: Basic dXNlcjpwYXNz

HTTP/1.1 200 Connection established

After the 200, the TLS handshake happens end to end between your client and the destination. The proxy relays ciphertext.

#What the proxy can and cannot see

  • Can see: the destination hostname and port, connection timing, and the volume of bytes transferred.
  • Cannot see: the URL path, headers, request body or response body.

This is why an HTTPS request through a proxy is far more private than a plain HTTP one — and why a proxy provider can still report which domains you contacted.

#Reference

CONNECT is defined in RFC 9110, which specifies current HTTP semantics.

Sources

  1. RFC 9110: HTTP Semantics (CONNECT)

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