We currently use a web-based login-portal which in turn is dependant on third-party authentication apps to log in to the MS Teams app for Android.
The way this works is that we have a login link like: authapp:///?token=12314&redirect=null which should open the third-party app and start the login, the issue is that the MS Teams app can't handle intent-links like authapp:/// and similar at all so we just get a generic error message during login.
I've tested this myself in my own app and the problem stems from the Android Webview component not having intent-handling built in like a browser would so instead MS Teams needs to implement a general handling of these links themselves (which is easy to do).
Wrote to support which basically told me it's out-of-scope and to write here instead, so here I am hoping a Microsoft dev sees this and can give an explanation as to why this isn't implemented.
Note: All of this works on iOS so it can't be intended for it to not work