As a developer, when a user clicks on an external url from within my app, I want to be able to force that url to open from within my app instead of in a new browser window so that I can implement an ideal UX flow for my app (eg. third party authentication). Acceptance Criteria: 1. Any url that is defined (based on the decided upon implementation) to open within the app that it lives within opens within that app 2. Any url that is not defined to open within the app that it lives within opens within in a new browser window
If bug 972320 gets implemented then the default behaviour inside app windows will be that links to URLs outside of the origin of the app manifest will open outside the app window (either in the system browser or in another app). There are use cases like third party authentication where this may not be what the app author wants so we could create a mechanism to allow certain off-origin navigations to stay inside the app window (or in future, the app's group of sheets).
One option is to add a list of URL prefixes to the app manifest to define which off-origin URLs open inside the app window. Another option is to require the use of a particular type of window.open call like using the "dialog" feature or specifying a particular target for window.open and hyperlinks, where the default behaviour is top open all off-origin URLs outside of the app.