Getting SSO to work on a hybrid mobile app is not quite standard as you have to do a bit of legwork to get it working.  I understand why XSUAA is something you are exploring as you will then be able to get your application to respect SAP authorisations without having to do anything fancy with users in one system mapping to another.

Here is a link to the SSO setup required on a Mendix hybrid app not SAP specific.  While it is not the exact answer you are after, I hope this will provide you with some pointers.

https://docs.mendix.com/howto/mobile/implement-sso-on-a-hybrid-app-with-mendix-and-saml

Good luck!