The Internet of Things (IoT) has improved people's lives by seamlessly integrating into many facets of modern life and facilitating information sharing across platforms. Device Authentication and Key exchange are major challenges for the IoT. High computational resource requirements for cryptographic primitives and message transmission during Authentication make the existing methods like PKI and IBE not suitable for these resource constrained devices. PUF appears to offer a practical and economical security mechanism in place of typically sophisticated cryptosystems like PKI and IBE. PUF provides an unclonable and tamper sensitive unique signature based on the PUF chip by using manufacturing process variability. Therefore, in this study, we use lightweight bitwise XOR, hash function, and PUF to Authenticate IoT devices. Despite several studies employing the PUF to authenticate communication between IoT devices, to the authors' knowledge, existing solutions require intermediary gateway and internet capabilities by the IoT device to directly interact with a Server for Authentication and hence, are not scalable when the IoT device works on different technologies like BLE, Zigbee, etc. To address the aforementioned issue, we present a system in which the IoT device does not require a continuous active internet connection to communicate with the server in order to Authenticate itself. The results of a thorough security study are validated against adversarial attacks and PUF modeling attacks. For formal security validation, the AVISPA verification tool is also used. Performance study recommends this protocol's lightweight characteristics. The proposed protocol's acceptability and defenses against adversarial assaults are supported by a prototype developed with ESP32.