No function key needed while calling Azure Function from Device Provisioning Service (DPS) for custom allocation

Question

We are using Azure IoT Hub Device Provisioning service which uses Azure function under custom allocation policy. Azure function with http trigger has authorization level as function with system managed identity disabled.

Below are the authentication settings in Azure function.

When I call this function using Bruno, I need to pass function key else I am getting 401 from function which is expected behaviour. But device provisioning service (DPS) calls Azure function without function key that part I couldn’t understand how DPS is able to call function without function key?

DPS where function is configured without function key: