QT does not work with OpenSSL 1.0 anymore. Versions QT 5.12.4 and above require OpenSSL 1.1, but fortunately OpenSSL 1.1 can be easily compiled with MS2017 as follows:
set PATH=%PATH%;C:\Perl64\bin set PATH=%PATH%;C:\PFiles\nasm-2.14.02-win64 perl Configure VC-WIN64A nmake
The key to the success is using ‘VS2017 x64 Native Tools Command Prompt‘, but not ‘VS2017 Developer Command Prompt’.
To make QT use OpenSSL, two dlls
should be copied to QT binary directory, for example, C:\Qt\Qt5.13.0\5.13.0\msvc2017_64\bin