It is possible too select as Admin - User Mode so the User permission, dictate the permissions allocated.
The permissions of the Apps Script Gadget can be set as follows:
The upload of files should be restricted by a simple pin / Capcha system to prevent malicious robot activity.
The Google Apps Script Gadget can be embedded from the Insert Menu.
An Uploader is harder to debug than other Business or cloud systems so creating a 'Blob' file to test is important. The following is a generic file for testing with a number to make it unique.
var rand = Math.random()*100000000000000000;
var Blob = Utilities.newBlob("Here is some data", "application/pdf", "FileUpload"+rand+".pdf");
Duplicate file uploads are given a assigned number. to overwrite a file you need find that specific filename to overwrite.
Some important considerations for Additional Features.
For Security Reasons Once you upload a file a generic pdf file with the Google Sites Uploader, the file will be created in the list below. In this example the Admin is the Active User.
It is also possible to upload to Google Drive simultaneously, or Email , or whatever service / API is available for you to access.
Multiple Apps Script Actions only require a single 'Blob' to be active in the cloud system then the 'Blob' can be define and can be sent, adjusted or edited.
A useful feature would be an Email Notification when a file is uploaded, or attached file/s depending on the Apps Script system required.
[App working but publicly disabled by permissions]