Https requests through proxy either hang or crash

Trying to make a https request through proxy which requires authentication causes the application to crash or to hang. It seems to always work fine for http requests.

It does not seem to matter if it is http or socks5 proxy, the crash happens in sendRequest() and in debug build an assert in qtbase/src/network/access/qhttpnetworkconnectionchannel.cpp, line 257 (Qt5.15.3) triggers.

This can be reproduced at least with CCProxy as the proxy server with Permit Only and Auth Type set to User/Password and some user defined. Then trying to run attached example.