Здравствуйте, lexile, Вы писали:

L>Хотя вот это:
L>

L>The client closes the connection to the proxy even if the proxy sends back the "Proxy-Connection: Keep-Alive" header for a CONNECT request.

L>в принципе, может быть причиной...

Есть предположение — в статье в мсдне сказано

To use a certificate contained in the collection, the application must have the same access rights
as the entity that issued the certificate

Попробуй гарантировать доступ к сертификату

This command grants access to the private key of the "MyCertificate" certificate in the "My" certificate store for the TESTUSER account.

winhttpcertcfg -g -c LOCAL_MACHINE\My -s MyCertificate -a TESTUSER