message: packages/app: add sign-in page
diff: * limitations under the License.
  */
  -import { createApp, AlertDisplay, OAuthRequestDialog } from '@backstage/core';
  +import {
  + createApp,
  + AlertDisplay,
  + OAuthRequestDialog,
  + SignInPage,
  +} from '@backstage/core';
  import React, { FC } from 'react';
  import Root from './components/Root';
  import * as plugins from './plugins';
  @@ -24,6 +29,11 @@ import { hot } from 'react-hot-loader/root';
  const app = createApp({
  apis,
  plugins: Object.values(plugins),
  + components: {
  + SignInPage: props => (
  + <SignInPage {...props} providers={['guest', 'google', 'custom']} />
  + ),
  + },
  });
  const AppProvider = app.getProvider();
  