Pronto does not do HTTPS.

You can do what I did for Flickr and stand up some man in the middle node js code on Raspberry pi that you can point Pronto to with HTTP and have it then send your request on to the https site.

I'd be happy to share a zip of the project but am not prepared to offer detailed support on installing nodejs on a pi or other platform and extreme configurations.

My code runs at /home/pi/node/httpsGateway and supports installing a systemctl service to start from this directory.

Example url requested by client:
http[colon-slash-slash]:<localhost>:<port>/https_get?cache_secs=<time in seconds>&target_url=<encoded https url to retrieve>

Note that cookies are not supported here. As a client, you will receive most response headers but current code does not support forwarding request headers.