Final answer:
Authentication in IoT typically involves an IoT device sending user credentials to a backend server, which authenticates and returns an authentication token. Alternative methods may include biometric verification if the devices support it.
Step-by-step explanation:
Authentication for mobile apps in IoT (Internet of Things) generally works through a process where the app communicates with a backend server to verify the user's credentials. While the exact method can vary, the most common involves option B, where the 'IoT device' sends the user's credentials to the backend server, which then authenticates them and sends back an authentication token. This token is then used to grant access to the device or service. Another approach is using biometrics (option D), but this largely depends on the capabilities of the mobile device and the IoT device. Option A is less secure as it exposes user credentials to the IoT device, and option C is less common for user authentication but might be used for securing communication between devices.