...
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.app_bar_main.*
import kotlinx.android.synthetic.main.nav_header_main.*

class MainActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelectedListener {

    override fun onCreate(savedInstanceState: Bundle?) {

        super.onCreate(savedInstanceState)

        val activityIntent: Intent
        // go straight to main if a token is stored
        if (!intent.hasExtra("email")) {
            activityIntent = Intent(this, LoginActivity::class.java)
            startActivity(activityIntent)
            finish()
        } else {
            setContentView(R.layout.activity_main)
            setSupportActionBar(toolbar)
            val toggle = ActionBarDrawerToggle(
                    this, drawer_layout, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close)
            drawer_layout.addDrawerListener(toggle)
            toggle.syncState()

            nav_view.setNavigationItemSelectedListener(this)
            email.text = intent.getStringExtra("email")
        }

    }

....
}