HTTP - Forward Proxy

A forward proxy is a proxy application that is configured to intercept and forward every internal Http request to an destination website, hence the name Forward Proxy.

It's also known as man-in-the-middle proxy.

The forward proxy sits on a local network between the local client (user) and the external destination website.

Technically, in order to get content from the origin server, the client sends a request to the forward proxy naming the origin server as the target. The proxy then requests the content from the origin server and returns it to the client.

A typical usage of a forward proxy is to intercept HTTP traffic and:

• to gives access to a public network to client on a private network
• to control the leaving traffic (ie provide HTTP access to internal clients that are otherwise restricted by a firewall)
• to implement a web cache to reduce network usage.
• to analyze HTTP traffic (Network - Trace (Capture|Sniffer|Analyzer) Tool (Packet Analysis))
• to modify the HTTP page
• to anonymize where the request originally came from

Example:

• Web Workers can intercept and modify HTTP request
• Security testing tool can intercept, modify and send traffic.
• Network - Trace (Capture|Sniffer|Analyzer) Tool (Packet Analysis)

The proxy can be implemented:

• on a intermediate server as a http server
• on the browser via a service worker

The client must be specially configured to use the forward proxy to access other sites. Ie the proxy parameters.

Example with Windows:

The configuration of a forward proxy on a Linux server happens with the environment variable http_proxy or https_proxy that set the proxy server location.

Example:

export http_proxy=http://proxy.example.com:8080
export https_proxy=https://proxy.example.com:8080