The recommended approach would indeed be to opt-out for a centralized login approach which would mean mobile uses using a system user-agent instead of directly authenticating in the mobile application. There even is passwordless authentication based on SMS which could be of use for you mobile scenario which coupled with account linking would mean end-users could register/authenticate in web application with a wide range of authentication options and then have a passwordless identity linked to their account so that they could authenticate in mobile just using a code received through SMS. However, this approach would mean the use of centralized login.
In conclusion, although it could be possible and somewhat linear to implement authentication embedded in the mobile application for database connections, any other authentication mechanism will likely imply a need for centralized login.