305 Use Proxy
Meaning
The requested resource is available only through a proxy, whose address is provided in the response. Many clients (browsers) do not support this response for security reasons.
When to Use
In older HTTP/1.1 usage, when a server wanted to indicate that the client must use a proxy to access the requested resource.
Example
A server returns 305 Use Proxy with a Location or Proxy-redirect header that instructs the client to use a specific proxy server for this resource.
When Not to Use
Do not use in modern applications. Most user-agents ignore 305 for security reasons, and it is deprecated in HTTP/1.1.
Source
RFC 2616 (deprecated)