Using a passport.js OAuth provider and using its oauth instance to access the API. (I wish there was a better way, but alas, there is not).

passport-oauth-api.js

// Uses passport-bitbucket
var strategy = new BitbucketStrategy({
    consumerKey: BITBUCKET_CONSUMER_KEY,
    consumerSecret: BITBUCKET_CONSUMER_SECRET,
    callbackURL: "http://127.0.0.1:3000/auth/bitbucket/callback"
  },
  function(token, tokenSecret, profile, done) {
    // asynchronous verification, for effect...
    process.nextTick(function () {
      api.setTokens(token, tokenSecret);
      return done(null, profile);
    });
  }
);
// Bitbucket is a light wrapper around the Bitbucket API that I wrote (not even close to complete).
// Any provider that is using passport-oauth (current version: 0.1.15), will have a ._oath property
var api = Bitbucket(strategy._oauth);