Research papers in lightweight authentication for the Internet of Things (IoT) focus on enabling secure and efficient identity verification for resource-constrained devices while minimizing computational, communication, and energy overhead. IoT networks consist of heterogeneous devices with limited processing power, memory, and battery life, making traditional authentication protocols like TLS/PKI-based schemes impractical. Researchers have proposed a variety of lightweight authentication mechanisms, including symmetric key-based methods using pre-shared keys (PSK) and message authentication codes (MACs), which offer fast and low-overhead verification but face challenges in key distribution and scalability. Public-key approaches based on Elliptic Curve Cryptography (ECC), including ECDH and ECDSA, are widely explored for providing strong security with smaller key sizes and reduced computational cost compared to RSA. Identity-based and certificate-less authentication schemes simplify key management by deriving public keys from unique device identities, reducing certificate handling and storage requirements. Token-based, one-time password (OTP), and challenge-response mechanisms are also studied for enhancing security in IoT applications such as smart homes, healthcare, and industrial monitoring. Recent works combine lightweight authentication with trust management, blockchain-assisted identity verification, and machine learning-based anomaly detection to improve resilience against insider attacks, spoofing, and replay attacks. Edge and fog computing paradigms are frequently integrated to offload authentication processing from constrained devices, enabling real-time verification while preserving device energy. Despite significant advancements, open challenges remain in achieving scalability, supporting dynamic device enrollment and revocation, and ensuring ultra-lightweight mechanisms for large-scale, heterogeneous IoT networks. Overall, the literature emphasizes that lightweight authentication is a cornerstone for securing IoT systems, balancing robust protection with the severe resource constraints inherent to these networks.