So today mal mentioned it and here are instructions
you gotta build new GitHub - mer-hybris/geoclue-providers-mlsdb which is no brainer if port is yours
and add /etc/gps_xtra.ini file with content
[MLS]
CUSTOM_URL=https://api.beacondb.net/v1/geolocate
CUSTOM_KEY=geoclue_sailfishos
That will probably arrive in next sfos release