I have kept the UI very minimal and focused more on the UX.
[L -> R]
Screen 1: The login page tells the user to log into his account, via options like username & password or social handles like Google or Facebook. It also has a link to Signup if the user doesn't have an account.
Screen 2: Authenticate Page detects it's a new device, tells the user about the security concern, and provides two options for 2-Factor Authorization. Option 1 - answering the security question and Option 2 - enter an OTP sent to the registered mobile number.
Screen 3: The server authenticates the user, with some confetti for celebration and provides a way to proceed to the app's homepage.