Allowed domains env variable for Google Auth (#682)

* Allowed domains env variable for Google Auth

* Fixing lint errors

* PR comments. Use includes instead of indexOf

server/pages/Home.js

@@ -10,7 +10,7 @@ import SigninButtons from './components/SigninButtons';
 import { developers, githubUrl } from '../../shared/utils/routeHelpers';
 
 type Props = {
-  notice?: 'google-hd' | 'auth-error',
+  notice?: 'google-hd' | 'auth-error' | 'hd-not-allowed',
   lastSignedIn: string,
   googleSigninEnabled: boolean,
   slackSigninEnabled: boolean,
@@ -38,6 +38,12 @@ function Home(props: Props) {
               try signing in with your company Google account.
             </Notice>
           )}
+          {props.notice === 'hd-not-allowed' && (
+            <Notice>
+              Sorry, your Google apps domain is not allowed. Please try again
+              with an allowed company domain.
+            </Notice>
+          )}
           {props.notice === 'auth-error' && (
             <Notice>
               Authentication failed - we were unable to sign you in at this