Achieving Zero Trust API Security: Leveraging Advanced OAuth Frameworks

The introduction of complex systems, particularly in the cloud and microservices, has made API security very critical. The traditional models of security based on protecting the outer perimeter are not proving very effective in the evolving environments. To counter, the Zero Trust security model that is centered around continuous verification of user and device identity has become popular. It is particularly essential for API defense, where the access has to be strictly managed to prevent unapproved use. OAuth, an extensively deployed authorization framework that makes secure access possible to resources without sharing credentials, is an essential component of it. Whereas OAuth 2.0 is adequate in managing API access, however, it is less suitable with a Zero Trust model, particularly when used with continuous verification and mitigating threats such as token compromise and misuse. Researchers have alleviated some of these challenges with proposals for enhanced OAuth extensions like Proof Key for Code Exchange (PKCE) and Mutual TLS (mTLS) to strengthen security in the Zero Trust setting. With such enhancements, even then, the research gaps for seamless OAuth- Zero Trust integration for flexible context-specific security remain significant. In this paper, we review work from 2015 to 2024 and illustrate the evolution of OAuth within the Zero Trust model, pinpointing key improvements, and cataloging the lingering challenges in defending APIs. Research indicates the demand for robust solutions, particularly within continuous authentication, real-time threat assessment, and adaptive token control. Bridging these gaps will be necessary in order to defend API interactions and ensure scalability for future distributed, cloud-native architectures.