sudo without password when logged in with SSH private keys

The option to do so has existed since (at least) April 2014.

You will need to install a package called pam_ssh_agent_auth (available for Centos 7 out of the box, YMMV), then configure /etc/pam.d/sudo to accept it as an authorization method. Finally, you may need to add SSH_AUTH_SOCK to the list of environment variables that persist during sudo.

The Gentoo wiki has details for these steps.