In recent years, Wireless Body Area Networks (WBANs) have witnessed rapid development, significantly facilitating remote medical monitoring and real-time health data collection. As the sensitivity of transmitted data increases, ensuring secure communication within WBANs has become a critical concern. Among various security mechanisms, authentication protocols play a vital role in protecting sensitive physiological information from unauthorized access. However, many existing protocols are not well-suited to the resource-constrained nature of WBAN devices, often suffering from high computational overhead and susceptibility to various attacks. To address these challenges, this paper proposes a lightweight authentication protocol that employs hash functions and XOR-based operations to achieve secure authentication and key agreement between the HN and sensor nodes (SNs). Informal security analysis and experimental results demonstrate that the proposed protocol effectively defends against common security threats in WBAN environments while maintaining low computational and communication overhead.