It is possible to request a URL in curl via proxy server using -x flag:

curl -x http://127.0.0.1:8080 https://google.com

This will send CONNECT request to your proxy server 127.0.0.1:8080. CONNECT request will ask proxy server to tunnel TCP connection to the destination. This means that, for example, proxy server won’t verify SSL certificate.

To force curl to send regular GET request, use the following command:

curl --request-target https://google.com -x 127.0.0.1:8080 127.0.0.1:8080