Support new authentication for GitHub #369
Description
Our GitHub authentication method is deprecated and will go away in November. See https://github.blog/2020-07-30-token-authentication-requirements-for-api-and-git-operations/ and https://twitter.com/patricktoomey/status/1289019204662972419. The simplest way is to have people generate a token, although we should try to do the localhost callback or device authorization flow if we can.