"graphene://middleauth+https://" protocol in a cloudpath does not work

[ceesem]

As part of the development of graphene integration in Neuroglancer, the auth protocol is provided to neuroglancer as an additional scheme: graphene://middleauth+https:// instead of just graphene://https://. Currently, however that gives the error:

Cloud Path must conform to [FORMAT://PROTOCOL://BUCKET/PATH](format://PROTOCOL//BUCKET/PATH)

For convenience in coming to cloudvolume from neuroglancer, it would be nice if this multi-scheme URL were acceptable and treated as equivalent to graphene://https://.