To do this, they require users to install a custom "trust root" (Certificate Authority (CA) certificate) in the client, and then the proxy terminates all TLS traffic from the client, impersonates the remote server and acts like a proxy. The proxy then sends back a generated certificate signed by the custom CA. Such proxy setups usually transparently capture all traffic from clients to TCP port 443 on a remote machine. Running curl in such a network would also get its HTTPS traffic captured.