Making passport compatible with graphql

[shalkam]

Hi,
So, in this commit I've enabled returning a value from the authenticate method of any strategy.
I've tested it with this strategy passport-graphql-mongoose that returns a promise instead of depending on callbacks.
I had to do this because if the authentication method is asynchronous, I always get an empty result and the callback takes effect only later on.
Now I can do something like this:

  async login(root, params, context, ast) {
    let res = {};
    if (typeof context.req.user === 'undefined') {
      context.req.body.username = params.username;
      context.req.body.password = params.password;
      const auth = passport.authenticate('local')(context.req);
      const user = await auth['local']
        .then(user => {
          context.req.logIn(user, function(err) {
            res = user;
            res.message = 'Logged in successfully!';
          });
        })
        .catch(err => {
          res = err;
        });
    } else {
      res = new Error('Already logged in');
    }
    return res;
  }

regards,
Mostafa

[coveralls]

Coverage increased (+0.004%) to 99.398% when pulling 9313e5b on shalkam:master into 8de1c66 on jaredhanson:master.