OAuth is an identity authentication and authorization protocol that allows applications to interact without requiring passwords, with OAuth1 and OAuth2 as its most popular iterations. OAuth1, introduced in 2006, facilitates user-approved application interactions through authorization tokens, enhancing security by eliminating the need for password sharing. However, it presents challenges such as a complex signature mechanism and token management issues. In 2012, OAuth2 was developed to address these issues, offering a more streamlined and flexible approach by employing Transport Layer Security (TLS) and creating distinct roles for resource and authorization servers. OAuth2 supports various use cases, including microservices, API gateways, and smart devices, and is more suitable for non-browser clients due to its simpler implementation and better security protocols. While OAuth1 remains relevant for high-security applications, OAuth2 has become the preferred choice for developers prioritizing ease of use and adaptability across different types of applications.