407 Proxy Authentication Required

Takeaways

1. Similar to 401 Unauthorized, but it indicates that the client needs to authenticate itself in order to use a proxy.
2. The proxy must send a Proxy-Authenticate header field containing a challenge applicable to that proxy for the target resource.
3. The client may repeat the request with a new or replaced Proxy-Authorization header field.

Example

HTTP/1.1 407 Proxy Authentication Required
Date: Wed, 21 Oct 2015 07:28:00 GMT
Proxy-Authenticate: Basic realm="Access to internal site"