407 Proxy Authentication Required HTTP Status Code

Description

HTTP status code 407 is defined as "Proxy Authentication Required". This status code is similar to 401 Unauthorized, but it indicates that the client must first authenticate itself with the proxy. When a client receives a 407 status code, it should understand that additional action needs to be taken by the user agent in order to fulfill the request. The response must include a Proxy-Authenticate header field containing a challenge applicable to the proxy for the target resource. This means that the request did not include the required authentication credentials for a proxy server that is between the user and the server that can fulfill the request. The client may repeat the request with suitable Proxy-Authorization header fields.

Status

HTTP

407 Proxy Authentication Required

Common Causes

The primary reasons for receiving a 407 HTTP status code include:

Authentication Required by Proxy: The client must first authenticate itself with the proxy. This is a standard requirement when the network's security policy mandates that all requests are routed through a proxy for monitoring, filtering, or other security reasons.
Incorrect or Missing Credentials: If the required proxy authentication credentials are incorrect or not provided in the request, the proxy server will respond with a 407 status code. This prompts the client to submit the correct credentials.
Unsupported Authentication Scheme: The proxy server might require authentication with a specific scheme (e.g., Basic, Digest, NTLM). If the client tries to authenticate using a scheme not supported by the proxy, it could lead to a 407 response.
Session Timeout or Invalid Session: In cases where the proxy server requires session-based authentication, a session timeout or an invalid session could trigger a 407 response. The client would then need to re-authenticate to establish a new session.
Configuration or Policy Changes on the Proxy: Changes in the proxy server's configuration or security policies could suddenly require authentication for requests that previously didn't need it, leading to unexpected 407 responses.
Network Infrastructure Changes: Alterations in network infrastructure, such as the introduction of a new proxy server or changes in the routing path, might subject requests to authentication requirements that weren't previously in place.

When a client receives a 407 status code, it should read the Proxy-Authenticate header in the response to understand the authentication scheme and realm expected by the proxy server. The client can then resend the request with the appropriate authentication credentials included in the Proxy-Authorization header.