Auth: searches don't work when signed-in via GitHub Enterprise

Created by: chrismwendt

• Run Sourcegraph 3.4.0-rc.4
• Add a GHE external service pointing to ghe.sgdev.org
• Configure sign-in via GitHub in the management console
• Sign in via GitHub
• Run a search for r:
• Notice this error:

When I sign in using built-in auth, that search works.

I noticed the URL is http://ghe.sgdev.org/api/v3/graphql but GitHub's GraphQL API is v4.