Low power wide area network (LPWAN) communication protocols are used in IoT (Internet of Things) devices to reduce energy consumption. LoRaWAN (Long range Wide Area Network) is one of the LPWAN technology that uses the LoRa modulation technique. The end devices (ED) can maintain a connection to the network even when they leave the range of their home network by using roaming in LoRaWAN version 1.1. However, there are also some limitations to LoRaWAN roaming. The major challenge is the security risk of data processing in an energy-efficient manner. This is because the visiting network server (vNS) needs to have access to the session information for the ED. This information is shared by the roaming ED to vNS through a plain text message and which is verified at the home network server (hNS). The chance of sniffing, replay, and impersonation attacks makes the existing system vulnerable. Also, the communication to hNS can be reduced if an ED verification mechanism exists at vNS. This paper presents an access authentication mechanism, SEC-ROAM, for vNS that enables secure data transmission between the end device and vNS and reduces the computation and communication cost of the network, enhancing the energy-efficient operation in LPWAN.