Update: This is a bug in GoogleDrive, CORS is not enabled for upload URIs. @Nivco pointed me to a work around with Google\'s client library which uses an i
It seems that you are right, the upload API endpoints don't seem to support CORS requests whereas the other endpoints do support it (sorry for not having tested thoroughly). This is a bug and we have let our engineering team know about the issue.
In the mean time it seems that the only workaround is to use the Javascript client library and take advantage of the iframe proxy it uses as described in Authorization of Google Drive using JavaScript
Thanks for bringing this up!