if your router supports DDNS (Most Do) I already have my sub domain configured to allow remote access to the WD EX 4 I have at home. You will need to setup DDNS and port forward without a static IP but I can access the WD UI using my subdomain and even remote into my server etc using the same sub domain the key is the port forwarding and the defined ports for each device.
When you say “login on WD my cloud”, what does that mean? Do you want to log into the WD My Cloud Dashboard?
One can use the MyCloud.com web portal to access their files on the My Cloud.
Currently one cannot officially access the single bay My Cloud Dashboard from outside their local network without using something like VPN. The My Cloud Dashboard will, as I understand it, reject any connection outside of the local IP address subnet. The single bay My Cloud and the WD EX4 are different units/models that may/probably have different firmware features/options.
Unofficially it may be possible. There is discussion in other threads that ask about Dashboard remote access, of using SSH to remote access the My Cloud Dashboard:
