At the moment it's not possible to block/allow connections from/to webservers based on the URL.

You can block/allow these servers based on their IP addresses.

Please pay attention:

1. if the server IP will be changed (e.g. provider change, server change) the URL will be available again until the rule will point to this IP

2. all websites hosted on this webserver cannot be reached as well

To avoid this you can use/configure a PROXY server for this and create a ruleset that allows http/https traffic only via this proxy

This specific situation is explained in the dedicated article Allow internet traffic via internal Proxy server only