Getting Custom MDM data in NEPacketTunnelProvider on iOS?

So we have our NEPacketTunnelProvider implementation and customers will be deploying it on their devices using MDM. All MDMs and Apple Configurator have VPN config section, where you can specify some Custom data as keys and values for Custom SSL VPN configuration. I can't figure it out how to read the data from NEPacketTunnelProvider subclass... Content Filters have filterConfiguration.vendorConfiguration to read custom data, but I can't find anything similar to get custom data from Tunnel Provider... Any hints?