If you're running WAMP and have recently installed cURL for command line and receive the error "The openssl extension is missing, which means that secure HTTPS transfer are impossible", then you'll need to enable the OpenSSL extension on your system.
WAMP uses different php.ini files for CLI (command line interface) and apache. To enable the OpenSSL extension on the command line version you'll need to browse to the php.ini file, on a default installation it will be in the following folder (version will need changing):
Browse to the line that reads:
...and remove the semicolon preceding the line. Restart your WAMP server services (click in your icon tray > 'Restart All Services' then open a new command line and retry the command that caused the error.