Allow providing accessTokens directly

It's possible to get access tokens from oauth providers through their javascript APIs. Because getting access tokens this way does not require browser redirects you can create an inline login screen by making the API call on the client, then passing the response to your server through an ajax call.

It's possible to get it to work with passport as is by replicating some of the authentication code in the request that provides the accessToken but it requires copying and pasting large chunks of anonymous functions. If passport provided a way to accept an accessToken directly it could be done much more cleanly.

No implementation files or tests are named in the issue. Start by tracing Passport’s existing authentication request flow and the code that handles access tokens obtained through redirects; compare that path with the described client-side token handoff. Done means an inline login can pass an access token to the server through a supported entry point without copying authentication logic.

Written by the indexing model from the issue text.