The HTTP 407 status code means a proxy requires authentication for the request.
The proxy server (also known as a gateway) sits between the client and the upstream server. Proxies can serve multiple purposes: caching, content filtering, security, TLS termination, performance improvement, etc…
This status code is similar to
401 Unauthorized, where the server wants the client to authenticate before proceeding with the request.
GET /secret HTTP/2
The only difference is that the proxy sends the
Proxy-Authenticate header when it wants clients to authenticate, instead of the
WWW-Authenticate header in 401.
HTTP/2 407 Proxy Authentication Required
Proxy-Authenticate: Basic realm="You Shall Not Pass"