RD Gateway authentication against remote domain

Hello forum,

I have a corporate internal network CORPDOMAIN and an environment in a datacenter with domain DCDOMAIN. There is no trust/forest between these two domains. In the datacenter I have a Remote Desktop Gateway (DCGW) used to access machines in the DCDOMAIN network.

What I want to achive is to enable users in CORPDOMAIN to authenticate against DCGW with their CORPDOMAIN accounts.

What are my options? I know that it would be possible to place a RODC of CORPDOMAIN into the DCDOMAIN environment and establish a trust, however this (at least to some point) weakens the securty of CORPDOMAIN - also because replication to RODC would take place over potentially insecure networks. 

I guess RADIUS would be the ideal solution but from what I read it is not supported with RD Gateway. 

What other viable options do exist?

Thanks!