message: backend: add example of setting up sign-in
diff: * limitations under the License.
  */
  -import { createRouter } from '@backstage/plugin-auth-backend';
  +import {
  + createRouter,
  + providers,
  + defaultAuthProviderFactories,
  +} from '@backstage/plugin-auth-backend';
  import { Router } from 'express';
  import { PluginEnvironment } from '../types';
  @@ -27,5 +31,13 @@ export default async function createPlugin(
  database: env.database,
  discovery: env.discovery,
  tokenManager: env.tokenManager,
  + providerFactories: {
  + ...defaultAuthProviderFactories,
  + google: providers.google.create({
  + signIn: {
  + resolver: providers.google.resolvers.byEmailLocalPart(),
  + },
  + }),
  + },
  });
  }
  