OAuth 2.0, a widely adopted open standard for authorization, is utilized by Kinde for secure and flexible authentication and authorization of applications. The text provides a historical overview of OAuth, detailing its evolution from its inception in 2007 to the release of OAuth 2.0, and highlights its adoption due to its robust security features and adaptability. Kinde supports both OpenID and OAuth 2.0, ensuring compatibility with a variety of authentication libraries without locking users into proprietary protocols. The document describes different client types—public and confidential—and their respective security considerations, with a focus on the use of JWT tokens for secure communication and the implementation of the PKCE extension to enhance the security of public clients. Kinde emphasizes the use of refresh tokens and token rotation to limit token exposure, enhancing security for both front-end and back-end authentication flows. Additionally, Kinde provides support for multi-API authentication, allowing applications to authorize multiple APIs with a single token, thereby enhancing the flexibility and scalability of the authentication process.