Is there a standard for using credentials from one web app to automatically log in to a partner app?

I am developing a web app that will be working with other companie开发者_Go百科s web apps. Part of the desired user experience is that users on our web application will be able to log into our app, and be able to visit our parters' web applications. Accounts will be automatically created for the users on our partners' sites. We'd like them to be able to enter the partner sites already authenticated, without having to log in or authorize anything (like with OpenID or OAuth), similar to the relationship between a bank and a credit card rewards program. Is there an existing standard that covers this?

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Single Sign On often used for such functionality.

There are a lot of implementations.

I used in production Jasig CAS