You are developing a Windows Store app that retrieves information from a social networking application by using web services. The web services require authentication. You need to recommend a solution

You are developing a Windows Store app that retrieves information from a social networking application by using web services. The web services require authentication. You need to recommend a solution to ensure that users are prompted for their credentials only the first time they use the app, even if the users are using the app from another device. What should you recommend?