Login failed for user '<token-identified principal>' with UAMI and Web App publish model Container

[bgiot]

The Web App has a user assigned managed identity.
That identity has access to the Azure sql server database (dbo role).
Env variable AZURE_CLIENT_ID is set with the client ID of the UAMI.
Connection string includes 'Authentication=Active Directory Default'
Still get login failed: Microsoft.Data.SqlClient.SqlException (0x80131904): Login failed for user ''.

Tried to use "Authentication=Active Directory Managed Identity; User Id=", but same error.
The docker image loaded is the default one from the Microsoft container registry - latest version.

Any clue to solve this ?