If you can't find a solution, take a look at the uTasker project. It supports posting files to the application or to the file system and also posting parameters. It operates with all browsers, as well as cURL. It also supports posting new (optionally encrypted) firmware to the target (boot loader).
This works on the M5223X and M5225X chips and can be completely tested in the uTaster simulator.
www.uTasker.com- OS, TCP/IP stack, USB, device drivers and simulator for M5221X, M5222X, M5223X, M5225X. One package does them all - "Embedding it better..."
Retrieving data ...