I'm building a teams app using the studio to wrap a set of SharePoint pages into an app.
Everything works fine on the web client of Microsoft Teams ans in the Teams app if the user preveously accessed SharePoint from the Microsoft Teams context. On both scenarios the autentication cookie is shared between SharePoint and the App.
If a new user adds the app on the Teams the autentication will fail on SharePoint because of the login page being displayed inside of an iframe.
Any alternative to authenticate SharePoint users using custom Apps on Microsoft Teams?