OAuth 2.0

Open Authorization (OAuth) is an open standard protocol that allows an end user’s credentials to access third party applications without exposing the user’s password. OAuth acts as the middle man to decide whether to allow end users access to third party applications. For example, say you want to access web application XYZ, and you do not have a user account for accessing this web application. However, XYZ has the option to allow you to log in using the credentials from a social media website ABC. So you access the website using the social media login.
For this to work, the application ‘XYZ’ is registered with ‘ABC’ and is an approved application. When you access XYZ, you use your user credentials for ABC. Then XYZ requests an access token from ABC on your behalf. Now you have access to XYZ. XYZ knows nothing about you and your user credentials, and this interaction is totally seamless for the user. Using secret tokens prevents a malicious application from getting your information and your data.