IoT is integrated with resource-restricted and tiny smart devices. IoT supports the devices to collect data from others, analyze and measure environmental features. However, CoAP communication is sensitive and leads to many security and privacy issues. Several authentication and encryption protocols have been suggested for CoAP in the provision of confidentiality and integrity. The authentication scheme should authenticate the devices on both sides securely and resource effectively. However, many authentication schemes for CoAP in IoT applications improve the metrics in security aspects, but mostly they degrade the performance-related metrics, due to resource constraint smart devices. It necessitates designing an efficient and lightweight security authentication scheme for CoAP.