Login failed. The login is from an untrusted domain and cannot be used with Integrated authentication

 SQL Error message typically occurs when trying to connect to a SQL Server using Windows Authentication, but the login attempt is coming from an untrusted domain. Here are several steps you can take to troubleshoot and resolve this issue:

1. Verify Network Connectivity:

   • Ensure that the client machine is properly connected to the network and can reach the SQL Server.

2. Check Domain Trust:

   • Make sure that the domain your client machine is on is trusted by the domain where the SQL Server resides. If the domains are not trusted, Windows Authentication cannot be used across them.

3. Verify SQL Server Configuration:

   • Ensure that SQL Server is configured to accept Windows Authentication.
   • Check the SQL Server settings to ensure it is not configured to use only SQL Server Authentication.

4. Check User Credentials:

   • Ensure the user trying to log in has the necessary permissions and is part of the correct domain.

5. Kerberos Authentication:

   • If using Kerberos authentication, verify that it is properly configured. Ensure that Service Principal Names (SPNs) are correctly set up for SQL Server.

6. Update SQL Server Configuration:

   • If possible, use SQL Server Authentication instead of Windows Authentication by providing a SQL Server login and password.

7. Local Machine Configuration:

   • Ensure the client machine is properly joined to the domain.
   • Check the local security policy settings and make sure they are configured to allow delegation.

Example of Changing Authentication Mode

If you decide to change the SQL Server to use mixed mode (both Windows Authentication and SQL Server Authentication), you can follow these steps:

1. Open SQL Server Management Studio (SSMS).
2. Connect to your SQL Server instance.
3. Right-click on the server in Object Explorer and select Properties.
4. In the Security page, under Server authentication, select SQL Server and Windows Authentication mode.
5. Click OK and restart the SQL Server service.

Example Connection String for SQL Server Authentication

string connectionString = "Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;";

If none of these steps resolve the issue, you may need to consult with your network administrator to ensure all domain trusts and network policies are correctly configured