Can we authenticate with Cognito and then Github?

**Describe the bug**
We are trying to leverage NetlifyCMS on an authenticated cognito user pool. How do we leverage Git-Gateway or OAuth Clients to get valid token for Github?

We tried [openid-wrapper](https://github.com/TimothyJones/github-cognito-openid-wrapper/issues/12), [Vencax's Oauth Client](https://github.com/vencax/netlify-cms-github-oauth-provider) and tried the [Github Oauth API](https://developer.github.com/apps/building-oauth-apps/authorizing-oauth-apps/)

Ideally we would like to map one github repo for all cognito users? or some other way to leverage CMS capabilities. We don't want to expose Github to our users. How do we achieve this? Any help will be highly appreciated

Thanks for building a great product!

Start by reviewing the Git-Gateway and OAuth Clients mentioned in the issue, along with the openid-wrapper, Vencax OAuth Client, and GitHub OAuth API references. Determine whether NetlifyCMS can support Cognito users without exposing GitHub, and document or implement a supported flow that maps users to one repository.

Written by the indexing model from the issue text.