Implement types for authentication strategies

[gr2m]

Blocked by octokit/octokit.js#2127

What’s missing?

THere is currently no way to define types for authentication strategy options:

new Octokit({
  authStrategy: createMyAuth,
  auth: myAuthOptions
})

Why?

It would be great to get the same intellisense as for the other options

Alternatives you tried

@weswigham layed out how this is possible to do in octokit/rest.js#13 (comment)

We plan to implement endpoints the same way, so we can remove the endpoint types from @octokit/types, and instead move it to an optional library, or multiple libraries even, so that we can provide the correct types for each GitHub Enterprise Server version.

This is going to be a bigger project.