Solved: Login failed for user ‘<token-identified principal>’ while authorizing to SQL Server via Service Principal from AAD group assigned

Are you tired of encountering the frustrating “Login failed for user ‘‘” error while trying to authenticate to SQL Server using a Service Principal from an AAD group assigned? Well, you’re not alone! This article is here to guide you through the solution to this pesky issue.

Understanding the Error

The error message “Login failed for user ‘‘” usually appears when your Service Principal, which is a part of an Azure Active Directory (AAD) group, tries to connect to a SQL Server instance. This error typically occurs due to incorrect configuration or missing permissions. But don’t worry, we’ll dive into the details and provide a step-by-step solution to resolve this issue.

Why is this error happening?

There are several reasons why you might encounter this error:

• Incorrect Azure AD application registration
• Missing or incorrect permissions on the SQL Server instance
• Invalid or expired tokens
• Incorrect configuration of the Service Principal

Step 1: Verify Azure AD Application Registration

To start troubleshooting, let’s ensure your Azure AD application is registered correctly:

1. Go to the Azure portal (https://portal.azure.com/) and sign in with your Azure account.
2. Navigate to the Azure Active Directory section.
3. Click on “App registrations” and search for your application.
4. Verify that the application has the necessary permissions, such as “Azure SQL Database” and “Windows Azure Active Directory.”

// Azure AD application registration example
{
  "appId": "YOUR_APP_ID",
  "appRoles": [],
  "availableToOtherTenants": true,
  "displayName": "YOUR_APP_NAME",
  "identifierUris": [
    "https://YOUR_TENANT_ID/YOUR_APP_ID"
  ],
  "replyUrls": [
    "https://YOUR_REDIRECT_URL"
  ],
  "requiredResourceAccess": [
    {
      "resourceAppId": "06b954b1-6060-4901-9be2-76c245cb71e1", // Azure SQL Database
      "resourceAccess": [
        {
          "id": "2623abd4-8a11-4939-a9d3-37323a548823",
          "type": "Scope"
        }
      ]
    },
    {
      "resourceAppId": "00000002-0000-0000-c000-000000000000", // Windows Azure Active Directory
      "resourceAccess": [
        {
          "id": "311a71cc-4851-49c9-8fcb-434ccc7a6291",
          "type": "Scope"
        }
      ]
    }
  ],
  "signInAudience": "AzureADandPersonalMicrosoftAccount"
}

Step 2: Grant Permissions on the SQL Server Instance

Ensure that your Service Principal has the necessary permissions on the SQL Server instance:

1. Connect to your SQL Server instance using SQL Server Management Studio (SSMS) or Azure Data Studio.
2. Execute the following T-SQL command to create a new login for the Service Principal:

CREATE LOGIN [YOUR_SERVICE_PRINCIPAL_NAME] FROM EXTERNAL PROVIDER;

This command creates a new login for the Service Principal using the external provider (Azure AD).

3. Grant the necessary permissions to the Service Principal login:

GRANT SELECT, EXECUTE, VIEW DATABASE STATE TO [YOUR_SERVICE_PRINCIPAL_NAME];

This grants the Service Principal the necessary permissions to interact with the SQL Server instance.

Step 3: Configure the Service Principal

Now, let’s configure the Service Principal to use the correct credentials:

1. Go back to the Azure portal and navigate to the Azure Active Directory section.
2. Click on “App registrations” and search for your application.
3. Click on “Certificates & secrets” and create a new client secret.
4. Copy the client secret value and store it securely (e.g., in an environment variable or a secure storage).

// Example Azure AD configuration for Service Principal
{
  "tenantId": "YOUR_TENANT_ID",
  "clientId": "YOUR_CLIENT_ID",
  "clientSecret": "YOUR_CLIENT_SECRET"
}

Step 4: Authenticate with the SQL Server Instance

Now that we’ve configured the Service Principal, let’s use it to authenticate with the SQL Server instance:

// Example C# code to authenticate with SQL Server using Service Principal
using System.Data.SqlClient;
using Microsoft.Azure.Services.AppAuthentication;
using Microsoft.Identity.Client;

// Create a new instance of the AzureServiceTokenProvider
var tokenProvider = new AzureServiceTokenProvider($"RunAs={YOUR_SERVICE_PRINCIPAL_NAME}");

// Get an access token for the SQL Server instance
var token = tokenProvider.GetAccessTokenAsync("https://database.windows.net/").Result;

// Create a new SqlConnection with the access token
using (var connection = new SqlConnection($"Data Source={YOUR_SQL_SERVER_INSTANCE};Initial Catalog={YOUR_DATABASE_NAME};"))
{
  connection.AccessToken = token.AccessToken;
  connection.Open();

  // Perform database operations
  SqlCommand command = new SqlCommand("SELECT * FROM [dbo].[YourTable]", connection);
  SqlDataReader reader = command.ExecuteReader();

  while (reader.Read())
  {
    Console.WriteLine($"Column value: {reader["YourColumnName"]}");
  }
}

Conclusion

By following these steps, you should be able to resolve the “Login failed for user ‘‘” error and successfully authenticate to your SQL Server instance using a Service Principal from an AAD group assigned. Remember to double-check your Azure AD application registration, grant necessary permissions on the SQL Server instance, configure the Service Principal correctly, and authenticate with the SQL Server instance using the access token.

Step	Description
1	Verify Azure AD application registration
2	Grant permissions on the SQL Server instance
3	Configure the Service Principal
4	Authenticate with the SQL Server instance

If you’re still encountering issues, make sure to check the Azure AD and SQL Server instance logs for more detailed error messages. Happy troubleshooting!

Additional Resources

• Create an Azure AD application and service principal in the portal
• Azure Active Directory authentication for SQL Server

By following these steps and resources, you should be able to resolve the “Login failed for user ‘‘” error and successfully integrate your Azure AD group assigned Service Principal with your SQL Server instance.

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