Currently I see that the Java buildpack and the PHP buildpack explicitly
mentioned in their doc that they can run behind a Web proxy, by setting the
HTTP_PROXY and HTTPS_RPOXY environment variable. And I suppose this is
supported in either the cached version or the uncached one, and for both
the old lucid64 stack and the new cflinuxfs2 stack (which has different
Ruby version). Do other buildpacks support the same? Aka node.js, python,
ruby, go, etc.

Thanks in advance!

Jack