Since build 5.2.792 it is possible to restrict Websocket client connections by certain domain or domains list with the following parameter in flashphoner.properties file
allow_domains=wcs.mydomain.com
There can be listed a number of domains and subdomains, they will be checked until the first match
allow_domains=mydomain.com,wcs.mydomain.com,myotherdomaincom,wcs2.myotherdomain.com
Mask ('*' character) is also supported, for example
allow_domains=*.mydomain.com,*.myotherdomain.com
Note that Websocket connection between CDN nodes are established by IP address, so all the CDN nodes addresses to connect to this server should be listed here when using this parameter on CDN node
allow_domains=*.mydomain.com,*.myotherdomain.com,192.168.111.101,192.168.111.102,192.168.112.1
The changes can be applied without restarting the server using CLI command
reload node-settings