What is openid connect authentication provider in Salesforce?

OpenID Connect is an interoperable authentication protocol based on the OAuth 2.0 family of specifications. It uses straightforward REST/JSON message flows with a design goal of “making simple things simple and complicated things possible”. It’s uniquely easy for developers to integrate, compared to any preceding Identity protocol. It uses any third-party web app that implements the server-side of the OpenID Connect protocol as an authentication provider, such as Amazon, Google, and PayPal.