App setting error when referencing keyvault secret on Function App using Linux Service Plan

We are unable to set an Application Setting on the Configuration section of a Function App v4 .NET 6 isolated process. This happens on a Linux App Service Plan.

The setting references a KeyVault secret in the format @Microsoft.KeyVault(SecretUri=https://myvaul.vault.azure.net/secrets/MySecret-ConnectionString/)

This works correctly on a Function App using a Windows App Service Plan. Both have user managed identity to access the appropriate KeyVault instance.

On the windows plan the setting shows with a green checkmark. On the linux plan the setting is shown with a red error marker.

Running the diagnostics and troubleshooting section is not helpful. It does not reveal any kind of error on the keyvault reference thus misleading the user.

[twentytwokhz]

@balag0 I think I narrowed it down to this topic

In my case there might be differences between windows function apps deployed via ARM templates and this particular linux function app which was created via Visual Studio Code advanced wizard.

The difference lies in the keyVaultReferenceIdentity property that I inspected on the Export template

• in the windows function app it was correctly referencing the user assigned managed identity
• in the linux function app (even though I set the user assigned managed identity in the Portal UI) the template shows a value of SystemAssigned

[twentytwokhz]

I executed the commands in the documentation with some minor tweaks (syntax was not working in cloud shell) and then the Key vault reference started working 🥇 🥳

Closing this since now it’s working… but please note this was NOT obvious at all. There is still room for improvement on the function app creation experience