OAuth (Open Authorization) is an open standard protocol used to provide secure, token-based access to resources without exposing user credentials. It allows third-party applications to access a user's data on other services, such as social media platforms or cloud providers, without the need to share their username and password. Instead of logging in directly, users grant permission to the third-party app to access specific data through an authorization server, which issues an access token. This token can then be used by the application to interact with the resource server (e.g., Google, Facebook) on behalf of the user.

OAuth 2.0, the most widely used version, is particularly prevalent in scenarios like single sign-on (SSO), where users can log into multiple services using a single set of credentials, and API integration, where third-party services need to interact with an application's data. The OAuth process enhances security by minimizing the risk of credential theft and giving users control over the scope and duration of the access they grant. However, implementing OAuth securely requires careful management of tokens, including their generation, storage, and expiration, to prevent vulnerabilities such as token leakage or unauthorized access.