Yes this is possible with Icecast as per that documentation. Icecast has a listener authentication feature which you can set up in the XML configuration (such as htpassword).
We would have to give you access to the control panels raw configuration file, which we can do. However, as far as we are aware only the URL based authentication might be possible as we don't have a way of giving you access to the file system for the htpasswd method at the moment we are afraid.
This is not something that we officially support by the way, so it's fine if you can get this working on your own but we can't help you much as we have not used it ourselves yet.
We did however recently have another user who tested this out and he stated that he got it working by navigating to the auth file in "/usr/local/centovacast/var/vhosts/username/" and he said that he added the following code below to one of the mount points before the closing </mount> and it was good to go. The username here being the main account username: