message: Update getting-started docs to provide sign in resolver
diff: @@ -187,6 +187,56 @@ components: {
  },
  ```
  +Since [v1.1.0](https://github.com/backstage/backstage/releases/tag/v1.1.0-next.3), you must provide an explicit sign-in resolver.
  +
  +Open `packages/backend/src/plugins/auth.ts` and replace with following code snippet:
  +
  +```typescript
  +import {
  + createRouter,
  + providers,
  + defaultAuthProviderFactories,
  +} from '@backstage/plugin-auth-backend';
  +import { Router } from 'express';
  +import { PluginEnvironment } from '../types';
  +import { stringifyEntityRef } from '@backstage/catalog-model';
  +
  +export default async function createPlugin(
  + env: PluginEnvironment,
  +): Promise<Router> {
  + return await createRouter({
  + ...env,
  + providerFactories: {
  + ...defaultAuthProviderFactories,
  + github: providers.github.create({
  + signIn: {
  + resolver: async ({ profile }, ctx) => {
  + if (!profile.email) {
  + throw new Error(
  + 'Login failed, user profile does not contain an email',
  + );
  + }
  + const [localPart] = profile.email.split('@');
  +
  + const userEntityRef = stringifyEntityRef({
  + kind: 'User',
  + name: localPart,
  + namespace: 'DEFAULT_NAMESPACE',
  + });
  + return ctx.issueToken({
  + claims: {
  + sub: userEntityRef,
  + ent: [userEntityRef],
  + },
  + });
  + },
  + },
  + }),
  + },
  + });
  +}
  +```
  +
  That should be it. You can stop your Backstage App. When you start it again and
  go to your Backstage portal in your browser, you should have your login prompt!
  