Add OpenID Connect support

[daikema]

Implement support for OpenID connect for authentication. (This issue is being added by request from @veggiesaurus to bring our offline discussions in sync).

An initial attempt was made at this with this pull request wherein the bulk of the work was done client-side, but this required that the identity providers supported public clients which doesn't always appear to be the case.

The oidc-serverside branch reimplements this, but implements most of the logic on the server-side so that identity providers that don't support public clients will also work.