This page describes the AutoQuad M4 CAN bus interface. Generic information about the AutoQuad CAN bus protocol is found here.
The AutoQuad M4 has a built in CAN port through a 2-pin JST SH connector.
When attached to an AutoQuad M4 Extension board this port is typically connected to a similar connector on the extension board, and the CAN port is then available at another connector that also carries 5V (typically used for powering the logic circuit on the ESC’s).
Can pin connection (Hi and Low) is documented next to the JST SH connector (CAN Hi is closest to the USB connector):