The go get fetching of source code is done by using one of the following tools expected to be found on your system:
- svn - Subversion, download at: https://subversion.apache.org/packages.html
- hg - Mercurial, download at https://www.mercurial-scm.org/downloads
- git - Git, download at https://git-scm.com/downloads
- bzr - Bazaar, download at https://wiki.bazaar.canonical.com/Download
For example, git is used for Github, hg is used for Bitbucket, etc.
Refer GoGetProxyConfig for setting proxies for these tools.