OAuth is an API-based authorization protocol that allows a third-party website to authorize access to a users data without the need for users to share their login credentials. It works its magic though the use of tokens. OAuth can get complex to implement, but the end result gives capabilities to Web-based services and apps that would not otherwise be possible. Google provides libraries to support these methods, though they exist mostly to prevent coder mishaps. The authentication process includes a screen describing the information that the user releases and the terms that apply.”]
Source: https://securityintelligence.com/about-oauth-use-for-api-authorization/