Make GitHub auth verify request through a proxy (#48)
Make GitHub auth verify request through a proxy (#48)

This matches the way GitHub API requests are made.

I haven't figured out a sensible way to test this, but we aren't testing
the other proxy uses either, so perhaps we can leave that aside for now.
canonical-ols/build.snapcraft.io,canonical-websites/build.snapcraft.io,canonical-websites/build.snapcraft.io,canonical-ols/build.snapcraft.io,canonical-websites/build.snapcraft.io,canonical-ols/build.snapcraft.io