A string. Source URN (objectId) for the file. Note the URN must be
Base64 encoded. To encode the URN, see, for example, the
jsonlite::base64_enc function.
token
A string. Token generated with getToken function
with data:read scope.
viewerType
A string. The type of viewer to instantiate. Either
"header" for the default viewer, "headless" for a viewer without toolbar
or panels, or "vr" to enter WebVR mode on a mobile device.