Tutorial: Connect to SQL Database from .NET App Service without secrets using a managed identity

Article
04/01/2023

App Service provides a highly scalable, self-patching web hosting service in Azure. It also provides a managed identity for your app, which is a turn-key solution for securing access to Azure SQL Database and other Azure services. Managed identities in App Service make your app more secure by eliminating secrets from your app, such as credentials in the connection strings. In this tutorial, you add managed identity to the sample web app you built in one of the following tutorials:

When you're finished, your sample app will connect to SQL Database securely without the need of username and passwords.

Architecture diagram for tutorial scenario.

Note

The steps covered in this tutorial support the following versions:

.NET Framework 4.8 and above
.NET 6.0 and above

For guidance for Azure Database for MySQL or Azure Database for PostgreSQL in other language frameworks (Node.js, Python, and Java), see Tutorial: Connect to Azure databases from App Service without secrets using a managed identity.

What you will learn:

Enable managed identities
Grant SQL Database access to the managed identity
Configure Entity Framework to use Azure AD authentication with SQL Database
Connect to SQL Database from Visual Studio using Azure AD authentication

Note

Azure AD authentication is different from Integrated Windows authentication in on-premises Active Directory (AD DS). AD DS and Azure AD use completely different authentication protocols. For more information, see Azure AD Domain Services documentation.

If you don't have an Azure subscription, create an Azure free account before you begin.

Prerequisites

This article continues where you left off in either one of the following tutorials:

If you haven't already, follow one of the two tutorials first. Alternatively, you can adapt the steps for your own .NET app with SQL Database.

To debug your app using SQL Database as the back end, make sure that you've allowed client connection from your computer. If not, add the client IP by following the steps at Manage server-level IP firewall rules using the Azure portal.

Prepare your environment for the Azure CLI.

Use the Bash environment in Azure Cloud Shell. For more information, see Quickstart for Bash in Azure Cloud Shell.
If you prefer to run CLI reference commands locally, install the Azure CLI. If you're running on Windows or macOS, consider running Azure CLI in a Docker container. For more information, see How to run the Azure CLI in a Docker container.
- If you're using a local installation, sign in to the Azure CLI by using the az login command. To finish the authentication process, follow the steps displayed in your terminal. For other sign-in options, see Sign in with the Azure CLI.
- When you're prompted, install the Azure CLI extension on first use. For more information about extensions, see Use extensions with the Azure CLI.
- Run az version to find the version and dependent libraries that are installed. To upgrade to the latest version, run az upgrade.

1. Grant database access to Azure AD user

First, enable Azure Active Directory authentication to SQL Database by assigning an Azure AD user as the admin of the server. This user is different from the Microsoft account you used to sign up for your Azure subscription. It must be a user that you created, imported, synced, or invited into Azure AD. For more information on allowed Azure AD users, see Azure AD features and limitations in SQL Database.

If your Azure AD tenant doesn't have a user yet, create one by following the steps at Add or delete users using Azure Active Directory.
Find the object ID of the Azure AD user using the az ad user list and replace <user-principal-name>. The result is saved to a variable.
```
azureaduser=$(az ad user list --filter "userPrincipalName eq '<user-principal-name>'" --query '[].id' --output tsv)
```
Tip

To see the list of all user principal names in Azure AD, run az ad user list --query '[].userPrincipalName'.
Add this Azure AD user as an Active Directory admin using az sql server ad-admin create command in the Cloud Shell. In the following command, replace <server-name> with the server name (without the .database.windows.net suffix).
```
az sql server ad-admin create --resource-group myResourceGroup --server-name <server-name> --display-name ADMIN --object-id $azureaduser
```

For more information on adding an Active Directory admin, see Provision an Azure Active Directory administrator for your server

2. Set up your dev environment

Visual Studio for Windows is integrated with Azure AD authentication. To enable development and debugging in Visual Studio, add your Azure AD user in Visual Studio by selecting File > Account Settings from the menu, and select Sign in or Add.
To set the Azure AD user for Azure service authentication, select Tools > Options from the menu, then select Azure Service Authentication > Account Selection. Select the Azure AD user you added and select OK.

Visual Studio for Mac is not integrated with Azure AD authentication. However, the Azure Identity client library that you'll use later can use tokens from Azure CLI. To enable development and debugging in Visual Studio, install Azure CLI on your local machine.
Sign in to Azure CLI with the following command using your Azure AD user:
```
az login --allow-no-subscriptions
```

The Azure Identity client library that you'll use later can use tokens from Azure CLI. To enable command-line based development, install Azure CLI on your local machine.
Sign in to Azure with the following command using your Azure AD user:
```
az login --allow-no-subscriptions
```

The Azure Identity client library that you'll use later can use tokens from Azure PowerShell. To enable command-line based development, install Azure PowerShell on your local machine.
Sign in to Azure CLI with the following cmdlet using your Azure AD user:
```
Connect-AzAccount
```

For more information about setting up your dev environment for Azure Active Directory authentication, see Azure Identity client library for .NET.

You're now ready to develop and debug your app with the SQL Database as the back end, using Azure AD authentication.

3. Modify your project

Note

Microsoft.Azure.Services.AppAuthentication is no longer recommended to use with new Azure SDK. It is replaced with new Azure Identity client library available for .NET, Java, TypeScript and Python and should be used for all new development. Information about how to migrate to Azure Identitycan be found here: AppAuthentication to Azure.Identity Migration Guidance.

The steps you follow for your project depends on whether you're using Entity Framework (default for ASP.NET) or Entity Framework Core (default for ASP.NET Core).

Entity Framework
Entity Framework Core

In Visual Studio, open the Package Manager Console and add the NuGet package Azure.Identity and update Entity Framework:
```
Install-Package Azure.Identity
Update-Package EntityFramework
```
In your DbContext object (in Models/MyDbContext.cs), add the following code to the default constructor.
```
var conn = (System.Data.SqlClient.SqlConnection)Database.Connection;
var credential = new Azure.Identity.DefaultAzureCredential();
var token = credential.GetToken(new Azure.Core.TokenRequestContext(new[] { "https://database.windows.net/.default" }));
conn.AccessToken = token.Token;
```
This code uses Azure.Identity.DefaultAzureCredential to get a useable token for SQL Database from Azure Active Directory and then adds it to the database connection. While you can customize DefaultAzureCredential, by default it's already versatile. When it runs in App Service, it uses app's system-assigned managed identity. When it runs locally, it can get a token using the logged-in identity of Visual Studio, Visual Studio Code, Azure CLI, and Azure PowerShell.
In Web.config, find the connection string called MyDbConnection and replace its connectionString value with "server=tcp:<server-name>.database.windows.net;database=<db-name>;". Replace <server-name> and <db-name> with your server name and database name. This connection string is used by the default constructor in Models/MyDbContext.cs.

That's every thing you need to connect to SQL Database. When you debug in Visual Studio, your code uses the Azure AD user you configured in 2. Set up your dev environment. You'll set up SQL Database later to allow connection from the managed identity of your App Service app.
Type Ctrl+F5 to run the app again. The same CRUD app in your browser is now connecting to the Azure SQL Database directly, using Azure AD authentication. This setup lets you run database migrations from Visual Studio.

In Visual Studio, open the Package Manager Console and add the NuGet package Microsoft.Data.SqlClient:
```
Install-Package Microsoft.Data.SqlClient -Version 5.1.0
```
In the ASP.NET Core and SQL Database tutorial, the MyDbConnection connection string in appsettings.json isn't used at all yet. The local environment and the Azure environment both get connection strings from their respective environment variables in order to keep connection secrets out of the source file. But now with Active Directory authentication, there are no more secrets. In appsettings.json, replace the value of the MyDbConnection connection string with:
```
"Server=tcp:<server-name>.database.windows.net;Authentication=Active Directory Default; Database=<database-name>;"
```
Note

The Active Directory Default authentication type can be used both on your local machine and in Azure App Service. The driver attempts to acquire a token from Azure Active Directory using various means. If the app is deployed, it gets a token from the app's managed identity. If the app is running locally, it tries to get a token from Visual Studio, Visual Studio Code, and Azure CLI.

That's everything you need to connect to SQL Database. When you debug in Visual Studio, your code uses the Azure AD user you configured in 2. Set up your dev environment. You'll set up SQL Database later to allow connection from the managed identity of your App Service app. The DefaultAzureCredential class caches the token in memory and retrieves it from Azure AD just before expiration. You don't need any custom code to refresh the token.
Type Ctrl+F5 to run the app again. The same CRUD app in your browser is now connecting to the Azure SQL Database directly, using Azure AD authentication. This setup lets you run database migrations from Visual Studio.

4. Use managed identity connectivity

Next, you configure your App Service app to connect to SQL Database with a system-assigned managed identity.

Note

While the instructions in this section are for a system-assigned identity, a user-assigned identity can just as easily be used. To do this. you would need the change the az webapp identity assign command to assign the desired user-assigned identity. Then, when creating the SQL user, make sure to use the name of the user-assigned identity resource rather than the site name.

Enable managed identity on app

To enable a managed identity for your Azure app, use the az webapp identity assign command in the Cloud Shell. In the following command, replace <app-name>.

az webapp identity assign --resource-group myResourceGroup --name <app-name>

Note

To enable managed identity for a deployment slot, add --slot <slot-name> and use the name of the slot in <slot-name>.

Here's an example of the output:

{
  "additionalProperties": {},
  "principalId": "21dfa71c-9e6f-4d17-9e90-1d28801c9735",
  "tenantId": "72f988bf-86f1-41af-91ab-2d7cd011db47",
  "type": "SystemAssigned"
}

Grant permissions to managed identity

Note

If you want, you can add the identity to an Azure AD group, then grant SQL Database access to the Azure AD group instead of the identity. For example, the following commands add the managed identity from the previous step to a new group called myAzureSQLDBAccessGroup:

groupid=$(az ad group create --display-name myAzureSQLDBAccessGroup --mail-nickname myAzureSQLDBAccessGroup --query objectId --output tsv)
msiobjectid=$(az webapp identity show --resource-group myResourceGroup --name <app-name> --query principalId --output tsv)
az ad group member add --group $groupid --member-id $msiobjectid
az ad group member list -g $groupid

In the Cloud Shell, sign in to SQL Database by using the SQLCMD command. Replace <server-name> with your server name, <db-name> with the database name your app uses, and <aad-user-name> and <aad-password> with your Azure AD user's credentials.
```
sqlcmd -S <server-name>.database.windows.net -d <db-name> -U <aad-user-name> -P "<aad-password>" -G -l 30
```
In the SQL prompt for the database you want, run the following commands to grant the minimum permissions your app needs. For example,
```
CREATE USER [<identity-name>] FROM EXTERNAL PROVIDER;
ALTER ROLE db_datareader ADD MEMBER [<identity-name>];
ALTER ROLE db_datawriter ADD MEMBER [<identity-name>];
ALTER ROLE db_ddladmin ADD MEMBER [<identity-name>];
GO
```
<identity-name> is the name of the managed identity in Azure AD. If the identity is system-assigned, the name is always the same as the name of your App Service app. For a deployment slot, the name of its system-assigned identity is <app-name>/slots/<slot-name>. To grant permissions for an Azure AD group, use the group's display name instead (for example, myAzureSQLDBAccessGroup).
Type EXIT to return to the Cloud Shell prompt.

Note

The back-end services of managed identities also maintains a token cache that updates the token for a target resource only when it expires. If you make a mistake configuring your SQL Database permissions and try to modify the permissions after trying to get a token with your app, you don't actually get a new token with the updated permissions until the cached token expires.

Note

Azure Active Directory and managed identities are not supported for on-premises SQL Server.

Modify connection string

Remember that the same changes you made in Web.config or appsettings.json works with the managed identity, so the only thing to do is to remove the existing connection string in App Service, which Visual Studio created deploying your app the first time. Use the following command, but replace <app-name> with the name of your app.

az webapp config connection-string delete --resource-group myResourceGroup --name <app-name> --setting-names MyDbConnection

5. Publish your changes

All that's left now is to publish your changes to Azure.

ASP.NET
ASP.NET Core

If you came from Tutorial: Build an ASP.NET app in Azure with SQL Database, publish your changes in Visual Studio. In the Solution Explorer, right-click your DotNetAppSqlDb project and select Publish.
In the publish page, select Publish.

Important

Ensure that your app service name doesn't match with any existing App Registrations. This will lead to Principal ID conflicts.

If you came from Tutorial: Build an ASP.NET Core and SQL Database app in Azure App Service, publish your changes using Git, with the following commands:

git commit -am "configure managed identity"
git push azure main

When the new webpage shows your to-do list, your app is connecting to the database using the managed identity.

Azure app after Code First Migration

You should now be able to edit the to-do list as before.

Clean up resources

In the preceding steps, you created Azure resources in a resource group. If you don't expect to need these resources in the future, delete the resource group by running the following command in the Cloud Shell: