Choose authentication method for QAuthenticator

Hi,

Background:

I'm the author of https://github.com/fedux-org/proxy_rb. This rubygem makes it easier to test HTTP-proxies in an automated fashion using `RSpec` (TDD in Ruby).

It uses capybara (https://github.com/jnicklas/capybara) in the background to give the use a nice API for testing his/her proxies. This project supports the use of "PhantomJS" (Adapter: Rubygem "poltergeist") and "Webkit" (Adapter: Rubygem "capybara-webkit") as driver.

Both projects seem to have "bindings" to Qt. I tried both Qt 4.x and 5.5.1 and get a similar behaviour. I'm a ruby developer, I'm not familar with Qt. I first tried to get support here https://github.com/thoughtbot/capybara-webkit/issues/882, but that was declined "as a problem" of Qt, but not the "capybara-webkit" library. That's why I opened this ticket to get advice/help.

Issue:

If a proxy server supports all schemes Bacis, NTLM, Kerberos, PhantomJS/Webkit (further named agent) chooses to use "NTLM" as authentication mechanism. But this fails.

1. Request from Agent to Proxy without credentials
2. Proxy rejects requests with 407
3. Agent starts NTLM authentication handshake
4. Authentication handshake fails with "wrong password" on the proxy side

Questions:

1. What kind of information do you use to generate the NTLM tokens?
2. Are there any environment variables etc. to gather more information for troubleshooting the issue?
3. Is there already an option similar to the one requested above, which I didn't find while searching your docs/issues.

Feature Request:

1. Would you mind to add an option to QAuthenticator (http://doc.qt.io/qt-5/qauthenticator.html#details) so that the user can choose the authentication scheme (Basic, NTLM, ...) which is used by the QAuthenticator

Thanks a lot.

Cheers,
Dennis