Simple file upload/download manager for distributing files

[coneroller]

I am looking for a simple, standalone file download solution in PHP for a company located in a rural area (slow internet connection) to distribute files to be downloaded by customers, press contacts, the printers', and so on, through their website which is hosted in a data center elsewhere. The perfect workflow would be:

• Admin users upload files
• Admin users determine who may access the file in one of these ways:
• The system creates a one-time access ID for the file, or
• the system has a simple permissions management to determine (external) users who are allowed to download the file
• The program returns a URL to copy+paste into an E-Mail
• The program keeps basic track of who downloaded what (optionally)

The file size is going to range between a few kilobytes and 10-20 Megabytes maximum. File types will be PDF and JPG mostly, with an occasional high-res image or Creative Suite file. I would probably want to make it single-sign-in capable together with the CMS that also runs on the package, so having the source code is a must, and good code readability a big plus. The server is a shared hosting package running on a LAMP stack.Hints are much appreciated.