Document Go proxy variables (HTTP_PROXY, HTTPS_PROXY, NO_PROXY)

[heitortsergent]

From a k6 blog post:

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"To have k6 send its traffic through a web proxy, we'll need to tell it on which TCP port the web proxy is listening.

Behind the scenes, k6 runs Go, and we use the built-in Go HTTP client for communication. Unlike some applications that use host OS proxy settings, Go programs depend on the presence of specific Environment Variables to determine whether to use a proxy and where it is listening. These magical Environment Variables are:

Name	Description
HTTP_PROXY	The proxy address given either as complete URL or as host:port that will be used for HTTP requests unless overwritten by NO_PROXY.
HTTPS_PROXY	The proxy address given either as complete URL or as host:port that will be used for HTTPS requests unless overwritten by NO_PROXY.
NO_PROXY	Hosts that should bypass proxies. This is a comma-separated string of IP addresses and/or host names. See the httpproxy docs for more info. Example: "1.2.3.4, 2.3.4.5:80, myhost.com"."