Fetch request method is not respected on iOS

[edeckers]

Describe the bug
Same issue as #158, but for download instead of upload.

The provided request method (HTTP verb) is not respected on iOS.

To Reproduce
Steps to reproduce the behavior:

1. Start a download from an iOS device with any method but GET
2. Check the access logs of the server and notice that regardless of the chosen method, data is received as a GET message

Expected behavior
The provided request method is used in the iOS code base, so the second reproduction step will show the actual chosen method.

Smartphone (please complete the following information):

• Device: all iOS
• OS: all iOS
• Browser: not applicable
• Version: all