Your question is Design Mobile User Authentication. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design the authentication flow for a mobile app. Your answer should cover how a user signs in, how credentials are exchanged for a session token, how the app stores and refreshes that token securely, and how logout invalidates the session.