Intemittent Login failed for user '<token-identified principal>'.","details":"SqlException: Login failed for user '<token-identified principal>

Question

Hello. We've an API running on Azure App Service that uses user assigned managed identity to authenticate against an Azure SQL DB.

The app works most of the time, no problem with authentication, however, we get an intermittent authentication issue like the one below:

Login failed for user '<token-identified principal>'.","details":"SqlException: Login failed for user '<token-identified principal>

Answer 1

Did you check the logs from both the Azure SQL Database and the App Service for patterns and specific times of failures?

You need to verify that the managed identity token is refreshed before it expires and that all instances of the App Service are correctly configured to use the managed identity, especially if scaling or instance restarts are involved.

Also, check if your managed identity has the necessary permissions on the SQL Database.

Verify if you have followed the steps mentioned in the standard documentation without any issue:

https://learn.microsoft.com/en-us/azure/data-factory/connector-azure-sql-managed-instance?tabs=data-factory#managed-identity

and successfully provisioned a Microsoft Entra administrator https://learn.microsoft.com/en-us/azure/azure-sql/database/authentication-aad-configure?view=azuresql&tabs=azure-powershell#provision-azure-ad-admin-sql-managed-instance for your Managed Instance?