Update the azure-easyauth provider docs for the new backend system

Signed-off-by: YAEGASHI Takeshi <yaegashi@gmail.com>

docs/auth/microsoft/azure-easyauth.md

@@ -7,62 +7,52 @@ description: Adding Azure's EasyAuth Proxy as an authentication provider in Back
 
 The Backstage `core-plugin-api` package comes with a Microsoft authentication provider that can authenticate users using Microsoft Entra ID (formerly Azure Active Directory) for PaaS service hosted in Azure that support Easy Auth, such as Azure App Services.
 
-## Backstage Changes
+## Backend Changes
 
-Add the following into your `app-config.yaml` or `app-config.production.yaml` file
+Add the following into your `app-config.yaml` under the root `auth` configuration:
 
-```yaml
+```yaml title="app-config.yaml"
 auth:
-  environment: development
   providers:
-    azure-easyauth: {}
+    azureEasyAuth:
+      signIn:
+        resolvers:
+          - resolver: idMatchingUserEntityAnnotation
+          - resolver: emailMatchingUserEntityProfileEmail
+          - resolver: emailLocalPartMatchingUserEntityName
 ```
 
-Add a `providerFactories` entry to the router in
-`packages/backend/src/plugins/auth.ts`.
+The `idMatchingUserEntityAnnotation` is
+[a builtin sign-in resolver](../identity-resolver.md#using-builtin-resolvers) from `azureEasyAuth` provider.
+It tries to find a user entity with [a `graph.microsoft.com/user-id` annotation](../../features/software-catalog/well-known-annotations.md#graphmicrosoftcomtenant-id-graphmicrosoftcomgroup-id-graphmicrosoftcomuser-id)
+which matches the object ID of the user attempting to sign in.
+If you want to provide your own sign-in resolver,
+see [Building Custom Resolvers](../identity-resolver.md#building-custom-resolvers).
 
-```ts
-import { providers } from '@backstage/plugin-auth-backend';
+Add the `@backstage/plugin-auth-backend-module-azure-easyauth-provider` to your backend installation.
 
-export default async function createPlugin(
-  env: PluginEnvironment,
-): Promise<Router> {
-  const authProviderFactories = {
-    'azure-easyauth': providers.easyAuth.create({
-      signIn: {
-        resolver: async (info, ctx) => {
-          const {
-            fullProfile: { id },
-          } = info.result;
+```sh
+# From your Backstage root directory
+yarn --cwd packages/backend add @backstage/plugin-auth-backend-module-azure-easyauth-provider
+```
 
-          if (!id) {
-            throw new Error('User profile contained no id');
-          }
+Then, add it to your backend's source,
 
-          return await ctx.signInWithCatalogUser({
-            annotations: {
-              'graph.microsoft.com/user-id': id,
-            },
-          });
-        },
-      },
-    }),
-  };
+```ts title="packages/backend/src/index.ts"
+const backend = createBackend();
 
-  return await createRouter({
-    logger: env.logger,
-    config: env.config,
-    database: env.database,
-    discovery: env.discovery,
-    tokenManager: env.tokenManager,
-    providerFactories: authProviderFactories,
-  });
-}
+backend.add(import('@backstage/plugin-auth-backend'));
+// highlight-add-next-line
+backend.add(
+  import('@backstage/plugin-auth-backend-module-azure-easyauth-provider'),
+);
+
+await backend.start();
 ```
 
 Now the backend is ready to serve auth requests on the
-`/api/auth/azure-easyauth/refresh` endpoint. All that's left is to update the frontend
-sign-in mechanism to poll that endpoint through the IAP, on the user's behalf.
+`/api/auth/azureEasyAuth/refresh` endpoint. All that's left is to update the frontend
+sign-in mechanism to poll that endpoint through the Easy Auth proxy, on the user's behalf.
 
 ## Frontend Changes
 
@@ -81,7 +71,7 @@ const app = createApp({
     SignInPage: props => {
       const configApi = useApi(configApiRef);
       if (configApi.getString('auth.environment') !== 'development') {
-        return <ProxiedSignInPage {...props} provider="azure-easyauth" />;
+        return <ProxiedSignInPage {...props} provider="azureEasyAuth" />;
       }
       return (
         <SignInPage