Connecting IoT devices to the IoT platform involves the three processes of attestation, authentication, and provisioning.

• The attestation mechanism represents the method chosen for a device to confirm its identity when it connects to an IoT platform service like Azure IoT Hub. IoT Hub supports symmetric key, X.509 thumbprint, and X.509 CA attestation methods.

• Authentication is how the device identifies itself. IoT Hub grants access to a device based on the device's ability to prove itself using its unique device identity in combination with its attestation mechanism.

• Provisioning is the act of enrolling a device into Azure IoT Hub. Provisioning makes IoT Hub aware of the device and the attestation mechanism the device uses.

https://learn.microsoft.com/en-us/azure/architecture/example-scenario/iot/attestation-provisioning