Allow disabling app services auth (Azure-Samples#1932)

* guidance on disabling app services auth for programmatic access

* Update docs/login_and_acl.md

* Update docs/login_and_acl.md

* Update docs/login_and_acl.md

* Update infra/main.bicep

---------

Co-authored-by: Pamela Fox <pamela.fox@gmail.com>

docs/login_and_acl.md

@@ -10,6 +10,7 @@
     - [Client App](#client-app)
     - [Configure Server App Known Client Applications](#configure-server-app-known-client-applications)
     - [Testing](#testing)
+    - [Programmatic Access With Authentication](#programmatic-access-with-authentication)
   - [Troubleshooting](#troubleshooting)
 - [Adding data with document level access control](#adding-data-with-document-level-access-control)
   - [Using the Add Documents API](#using-the-add-documents-api)
@@ -35,7 +36,7 @@ Two Microsoft Entra applications must be registered in order to make the optiona
 
 The easiest way to setup the two apps is to use the `azd` CLI. We've written scripts that will automatically create the two apps and configure them for use with the sample. To trigger the automatic setup, run the following commands:
 
-1. Run `azd env set AZURE_USE_AUTHENTICATION true` to enable the login UI and App Service authentication.
+1. Run `azd env set AZURE_USE_AUTHENTICATION true` to enable the login UI and use App Service authentication by default.
 1. Ensure access control is enabled on your search index. If your index doesn't exist yet, run prepdocs with `AZURE_USE_AUTHENTICATION` set to `true`. If your index already exists, run `pwsh ./scripts/manageacl.ps1 --acl-action enable_acls`.
 1. (Optional) To require access control when using the app, run `azd env set AZURE_ENFORCE_ACCESS_CONTROL true`. Authentication is always required to search on documents with access control assigned, regardless of if unauthenticated access is enabled or not.
 1. (Optional) To allow authenticated users to search on documents that have no access controls assigned, even when access control is required, run `azd env set AZURE_ENABLE_GLOBAL_DOCUMENT_ACCESS true`.
@@ -134,6 +135,21 @@ Ensure you run `azd env set AZURE_USE_AUTHENTICATION` to enable the login UI onc
 
 In both the chat and ask a question modes, under **Developer settings** optional **Use oid security filter** and **Use groups security filter** checkboxes will appear. The oid (User ID) filter maps to the `oids` field in the search index and the groups (Group ID) filter maps to the `groups` field in the search index. If `AZURE_ENFORCE_ACCESS_CONTROL` has been set, then both the **Use oid security filter** and **Use groups security filter** options are always enabled and cannot be disabled.
 
+#### Programmatic Access with Authentication
+
+If you want to use the chat endpoint without the UI and still use authentication, you must disable [App Service built-in authentication](https://learn.microsoft.com/azure/app-service/overview-authentication-authorization) and use only the app's MSAL-based authentication flow. Ensure the `AZURE_DISABLE_APP_SERVICES_AUTHENTICATION` environment variable is set before deploying.
+
+Get an access token that can be used for calling the chat API using the following code:
+
+```python
+from azure.identity import DefaultAzureCredential
+import os
+
+token = DefaultAzureCredential().get_token(f"api://{os.environ['AZURE_SERVER_APP_ID']}/access_as_user", tenant_id=os.getenv('AZURE_AUTH_TENANT_ID', os.getenv('AZURE_TENANT_ID')))
+
+print(token.token)
+```
+
 ### Troubleshooting
 
 - If your primary tenant restricts the ability to create Entra applications, you'll need to use a separate tenant to create the Entra applications. You can create a new tenant by following [these instructions](https://learn.microsoft.com/entra/identity-platform/quickstart-create-new-tenant). Then run `azd env set AZURE_AUTH_TENANT_ID <YOUR-AUTH-TENANT-ID>` before running `azd up`.
@@ -235,6 +251,7 @@ The following environment variables are used to setup the optional login and doc
 - `AZURE_ENFORCE_ACCESS_CONTROL`: Enforces Entra ID based login and document level access control on documents with access control assigned. Set to true before running `azd up`. If `AZURE_ENFORCE_ACCESS_CONTROL` is enabled and `AZURE_ENABLE_UNAUTHENTICATED_ACCESS` is not enabled, then authentication is required to use the app.
 - `AZURE_ENABLE_GLOBAL_DOCUMENT_ACCESS`: Allows users to search on documents that have no access controls assigned
 - `AZURE_ENABLE_UNAUTHENTICATED_ACCESS`: Allows unauthenticated users to access the chat app, even when `AZURE_ENFORCE_ACCESS_CONTROL` is enabled. `AZURE_ENABLE_GLOBAL_DOCUMENT_ACCESS` should be set to true to allow unauthenticated users to search on documents that have no access control assigned. Unauthenticated users cannot search on documents with access control assigned.
+- `AZURE_DISABLE_APP_SERVICES_AUTHENTICATION`: Disables [use of built-in authentication for App Services](https://learn.microsoft.com/azure/app-service/overview-authentication-authorization). An authentication flow based on the MSAL SDKs is used instead. Useful when you want to provide programmatic access to the chat endpoints with authentication.
 - `AZURE_SERVER_APP_ID`: (Required) Application ID of the Microsoft Entra app for the API server.
 - `AZURE_SERVER_APP_SECRET`: [Client secret](https://learn.microsoft.com/entra/identity-platform/v2-oauth2-client-creds-grant-flow) used by the API server to authenticate using the Microsoft Entra server app.
 - `AZURE_CLIENT_APP_ID`: Application ID of the Microsoft Entra app for the client UI.

infra/core/host/appservice.bicep

@@ -48,6 +48,7 @@ param authenticationIssuerUri string = ''
 @allowed([ 'Enabled', 'Disabled' ])
 param publicNetworkAccess string = 'Enabled'
 param enableUnauthenticatedAccess bool = false
+param disableAppServicesAuthentication bool = false
 
 var msftAllowedOrigins = [ 'https://portal.azure.com', 'https://ms.portal.azure.com' ]
 var loginEndpoint = environment().authentication.loginEndpoint
@@ -134,7 +135,7 @@ resource appService 'Microsoft.Web/sites@2022-03-01' = {
     }
   }
 
-  resource configAuth 'config' = if (!(empty(clientAppId))) {
+  resource configAuth 'config' = if (!(empty(clientAppId)) && !disableAppServicesAuthentication) {
     name: 'authsettingsV2'
     properties: {
       globalValidation: {

infra/main.bicep

@@ -128,6 +128,9 @@ param authTenantId string = ''
 // Used for the optional login and document level access control system
 param useAuthentication bool = false
 param enforceAccessControl bool = false
+// Force using MSAL app authentication instead of built-in App Service authentication
+// https://learn.microsoft.com/azure/app-service/overview-authentication-authorization
+param disableAppServicesAuthentication bool = false
 param enableGlobalDocuments bool = false
 param enableUnauthenticatedAccess bool = false
 param serverAppId string = ''
@@ -276,6 +279,7 @@ module backend 'core/host/appservice.bicep' = {
     clientAppId: clientAppId
     serverAppId: serverAppId
     enableUnauthenticatedAccess: enableUnauthenticatedAccess
+    disableAppServicesAuthentication: disableAppServicesAuthentication
     clientSecretSettingName: !empty(clientAppSecret) ? 'AZURE_CLIENT_APP_SECRET' : ''
     authenticationIssuerUri: authenticationIssuerUri
     use32BitWorkerProcess: appServiceSkuName == 'F1'

infra/main.parameters.json

@@ -179,6 +179,9 @@
     "enforceAccessControl": {
       "value": "${AZURE_ENFORCE_ACCESS_CONTROL=false}"
     },
+    "disableAppServicesAuthentication": {
+      "value": "${AZURE_DISABLE_APP_SERVICES_AUTHENTICATION=false}"
+    },
     "enableGlobalDocuments": {
       "value": "${AZURE_ENABLE_GLOBAL_DOCUMENT_ACCESS=false}"
     },