To configure a login screen for SAP Fiori launchpad, follow the steps described in the topic Login Screen for the Launchpad (see SAP Library for User Interface Add-On 2.0 for SAP NetWeaver on SAP Help Portal at http://help.sap.com/nw-uiaddon).
If you want to configure a login screen for your standalone app, replace your namespace and your app name in step 3 of the topic Login Screen for the Launchpad:
Navigate to <your app name>
and double-click