An authentication controller coupled to a first communication port of a portable computing device is allowed to provide authentication on behalf of an accessory device coupled to a second communication port of the portable computing device. In one embodiment, a dongle that includes an authentication controller can be coupled with the portable computing device. Accessory devices can also be coupled with the potable computing device through other ports, including wireless ports. The dongle can provide cross-transport authentication for accessories that do not include authentication controllers. Once the dongle had been properly authenticated, the permissions granted to the dongle port can be transferred to a communication port coupled with an accessory.