PitawatNantamanop-3754, Thanks for the great question! While I check on this internally/request anthonychu-msft (our Azure Static Web Apps PG) for additional insights.
As mentioned in this FAQ: 'Does Static Web Apps support managed identity?'
"Static Web Apps supports managed identity, but it's only used to retrieve authentication secrets from Key Vault.
If you need managed identity or Key Vault references in your API, use the bring your own Functions app feature to use a separate Functions app that uses managed identity."