OAuth2 support

[rospe]

Hi,

it'd be great if your library would support OAuth2 auth flow for specific URLs, since all our $refs are secured by that method. For example, we could provide client credentials (clientid and client secret + token endpoint) via ENV and would then expect that the library requests a bearer token and send it along in the header for the respective requests to our selected referred URLs.

[gazpachoking]

This isn't something that would be included directly in the library, but it should be fairly easy to implement yourself. You can write a custom loader to grab the references and return the loaded json.