Qt/C++ getting OS proxy settings - c++

Question

I need to retrieve the proxy settings on Windows. They have been set by an admin, so they reside in the registry at locations:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\CurrentVersion\Internet Settings
ProxySettingsPerUser = 0x00000000 (0)
This entry is giving the information whether the proxy settings need to be read from HKCU(ProxySettingsPerUser=1) or HKLM(ProxySettingsPerUser=0).
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings
ProxyEnable = 0x00000001 (1)
ProxyServer = Host:Port
When I try to read them directly, the default value/string is returned (i.e. not the actual contents of the variable):
Code:
#define HKLM_INTERNET_SETTINGS_KEY "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Internet Settings"
//[...]
QSettings regHKLM( HKLM_INTERNET_SETTINGS_KEY, QSettings::NativeFormat );
QString read = regHKLM.value( "ProxyServer", "default" ).toString();
logDebug(QString("ProxyServer %1").arg(read));
Other entries in the same location, such as CodeBaseSearchPath = "CODEBASE" or WarnOnIntranet = 0x00000001 (1), can be read without a problem.
THe second approach tried was to read the proxy settings by using the MSDN functions ::WinHttpGetIEProxyConfigForCurrentUser and ::WinHttpGetProxyForUrl. The code is working fine when trying to read HKCU settings (given both manually host-port or as pac file). But when the settings need to be retrieved from HKLM, the following error is returned:
ERROR_WINHTTP_AUTODETECTION_FAILED
12180
Returned by WinHttpDetectAutoProxyConfigUrl if WinHTTP was unable to discover the URL of the Proxy Auto-Configuration (PAC) file.
Is there another approach to retrieving the HKLM proxy settings?
If the approaches described above should have worked, is there a special condition/privilage that needs to be fulfilled before the settings can be read? (in the first approached, the application already has elevated the privilage level to maximum possible, and the manifest file is set to level "asInvoker")
Best regards,
Kornrade