HTTP 407 – Proxy Authentication Required
Similar to 401, but authentication is needed with a proxy first.
Common use case
Seen inside corporate networks where traffic must pass through an authenticating forward proxy before reaching the internet.
Example
HTTP/1.1 407 Proxy Authentication Required
Proxy-Authenticate: Basic
History
Part of the original HTTP/1.1 spec, RFC 2068 (1997).
Did you know?
Most end users never see it directly - it is usually handled silently by browser or OS-level proxy authentication dialogs.