Securing authentication in the Web of Things (WoT) is increasingly complex, with traditional Single Sign-On (SSO) systems presenting vulnerabilities like single points of failure and and data breaches. This chapter introduces a blockchain-based SSO framework using Ethereum smart contracts to decentralize authentication. By removing central authorities, the system enhances security, ensures data integrity, and improves user control over credentials. Leveraging blockchain’s cryptography, it offers tamper-proof authentication and mitigates credential theft and cyber threats. The chapter details the system’s architecture, demonstrating how blockchain-based decentralization addresses traditional SSO weaknesses. It highlights benefits like improved resilience, faster authentication, and enhanced privacy through the elimination of intermediaries. Testing results validate the system’s reliability, scalability, and practicality for securing WoT networks. The chapter argues that blockchain’s decentralized control and secure identity management are promising for WoT ecosystems. Combining blockchain’s transparency and security with WoT’s distributed nature empowers autonomous user identity management, reducing unauthorized access and data misuse. This decentralized approach seamlessly integrates with WoT environments requiring secure device communication. Real-world applications illustrate the design, implementation, and implications of blockchain-based SSO for WoT security, demonstrating its potential for a more secure, user-centric digital future.