Authentication system with an automatic authentication mechanism and automatic authentication method

An authentication system with an automatic authentication mechanism comprising:

• a server device;
• a gateway device, coupled to the server device;
• and
• a user device, coupled to the gateway device,
• wherein the gateway device is configured to act as a fast identity online (FIDO) client based on a FIDO protocol to send a gateway device registration data to register the gateway device in the server device acting as a FIDO server, and then the gateway device defines itself as initialized and connected,
• wherein the gateway device periodically sends data to the server device for authentication to maintain a trusted connection between the server device and the gateway device based on the FIDO protocol,
• wherein when the user device, based on the FIDO protocol, performs a registration operation, the user device acts as the FIDO client to send a user device registration data to the gateway device acting as the FIDO server, and the gateway device determines whether the user device is successfully registered by checking the user device registration data.