httpstatuses/contents/codes/407.md

set	code	title	references
4	407	Proxy Authentication Required	Rails HTTP Status Symbol :proxy_authentication_required

The 407 (Proxy Authentication Required) status code is similar to 401 (Unauthorized), but it indicates that the client needs to authenticate itself in order to use a proxy. The proxy MUST send a Proxy-Authenticate header field (Section 4.3) containing a challenge applicable to that proxy for the target resource. The client MAY repeat the request with a new or replaced Proxy-Authorization header field (Section 4.4).

Source: RFC7235 Section 3.2