The integration of Distributed Energy Resources (DERs) into modern power systems is often limited by heterogeneous communication protocols and manufacturer-specific data representations. This paper presents DERway, an edge interoperability gateway that provides bidirectional communication between DER devices and grid-facing applications. DERway supports southbound protocols including Modbus TCP/IP, Modbus RTU, and CAN, while exposing telemetry and control capabilities through MQTT and REST interfaces. The gateway follows a modular architecture in which device-specific communication and data transformations are decoupled from upper-layer modules through an \textit{Internal MQTT Broker}. Device integration is primarily configuration-based, with scripting support for manufacturer-specific decoding and transformations. DERway is experimentally validated in X-Energy Lab, a reconfigurable smart-grid laboratory from INESC TEC, against four real DER devices spanning all three supported field protocols: two batteries over Modbus TCP/IP, a heat pump over Modbus RTU, and a DC-DC EV charger over CAN. The results show that the same architecture sustains weeks-long telemetry acquisition with over 99\% reading delivery and confirms bidirectional setpoint control within a few polling cycles, without protocol-specific changes outside each device's own configuration, demonstrating the feasibility of a common edge gateway architecture for heterogeneous DER communication.