https://userapps.support.sap.com/sap/support/knowledge/en/2485474
2485474 - How to configure SSO from Fiori Launchpad to a back-end system in a HUB environment | SAP...
Launching a Web Dynpro or SAP GUI for HTML application from Fiori Launchpad returns a logon screen to request user name and password of the back-end system. OR...