Check out Google's SUPL client:
https://github.com/google/supl-client

You can see it's use in GnssLogger here:
https://github.com/google/gps-measurement-tools/blob/53f9105742426a64373840ffacd81e6a7c9c0df9/GNSSLogger/pseudorange/src/main/java/com/google/location/lbs/gnss/gps/pseudorange/PseudorangePositionVelocityFromRealTimeEvents.java#L367