add microsoft azure auth provider + add to example app

plugins/auth-backend/README.md

@@ -74,6 +74,41 @@ export AUTH_AUTH0_CLIENT_ID=x
 export AUTH_AUTH0_CLIENT_SECRET=x
 ```
 
+### Microsoft
+
+#### Creating an Azure AD App Registration
+
+An Azure AD App Registration is required to be able to sign in using Azure AD and the Microsoft Graph API.  
+Click [here](https://portal.azure.com/#blade/Microsoft_AAD_IAM/ActiveDirectoryMenuBlade/RegisteredApps) to create a new one.
+
+- Click on the `New Registration` button.
+- Give the app a name. e.g. `backstage-dev`
+- Select `Accounts in this organizational directory only` under supported account types.
+- Enter the callback URL for your backstage backend instance:
+   - For local development, this is likely `http://localhost:7000/auth/microsoft/handler/frame`
+   - For non-local deployments, this will be `https://{APP_FQDN}:{APP_BACKEND_PORT}/auth/microsoft/handler/frame`
+- Click `Register`.
+
+We also need to generate a client secret so Backstage can authenticate as this app.
+
+- Click on the `Certificates & secrets` menu item.
+- Under `Client secrets`, click on `New client secret`.
+- Add a description for the new secret. e.g. `auth-backend-plugin`
+- Select an expiry time; `1 Year`, `2 Years` or `Never`.
+- Click `Add`.
+
+The secret value will then be displayed on the screen. **You will not be able to retrieve it again after leaving the page**.
+
+#### Starting the Auth Backend
+
+```bash
+cd packages/backend
+export AUTH_AZURE_CLIENT_ID=x
+export AUTH_AZURE_CLIENT_SECRET=x
+export AUTH_AZURE_TENANT_ID=x
+yarn start
+```
+
 ### SAML
 
 To try out SAML, you can use the mock identity provider: