As an admin, I want to be able to login, so I can access the admin interface

[jboxman]

This must be our initial effort. However a user account is defined, we'll decide that here.

It's important to note that, because GitHub does not support the client OAuth flow, this must live outside of the SPA itself. (I came up with a fun hack to work around this, but that's way beyond the scope of this project.)

Acceptance criteria

• A user is presented with a login button/link that redirects to GitHub OAuth2 to perform user authentication/new account creation
• If a user does not yet exist, the user object is created in MongoDB automatically and the user authentication token is updated accordingly (passport does everything but handle User.find and User.create)
• If a user does exist, the user authentication token is updated accordingly (passport does this based on User model)

[jboxman]

// http://scottksmith.com/blog/2014/09/18/beer-locker-building-a-restful-api-with-node-username-and-password/
const passport = require('koa-passport');
const GitHubStrategy = require('passport-github2').Strategy;
const MockStrategy = require('./mock-strategy').Strategy;

const User = require('../backend/entities/users/userModel');

function onSuccess(accessToken, refreshToken, profile, done) {
  // https://stackoverflow.com/questions/20431049/what-is-function-user-findorcreate-doing-and-when-is-it-called-in-passport
  User.findOrCreate(
    {
      oauthId: profile.id
    },
    {
      oauthId: profile.id,
      oauthProvider: profile.provider,
      email: profile.emails[0].value,
      username: profile.username,
      avatarUrl: profile._json.avatar_url
    },
    function(error, user, created) {
      done(null, user.toJSON());
  });
}

function strategyForEnvironment() {
  let strategy;
  switch(process.env.NODE_ENV) {
    case 'production':
     strategy = new GitHubStrategy({
        clientID: process.env.CLIENT_ID,
        clientSecret: process.env.CLIENT_SECRET,
        callbackURL: process.env.CALLBACK_URL
      }, onSuccess);
    break;
    default:
      strategy = new MockStrategy('github', onSuccess);
  }
  return strategy;
}

passport.serializeUser(function(user, done) {
  done(null, user.id);
});

// TODO - Sad path, user ID doesn't exist, possibly because it was deleted
passport.deserializeUser(async function(id, done) {
  try {
    const user = await User.findById(id).exec();
    done(null, user.toJSON());
  }
  catch(err) {
    done(err);
  }
});

passport.use(strategyForEnvironment());