To use an external application link you'd need to organise how to provide a username and password as part of the link you copy into the page in VOICE with the external service provider. It's not something that the VOICE platform can do on it's side because of the nature of how the web works.
So you'll need to speak to the service provider and ask them what provision there is for supplying a username and password with requests.
I hope that helps but if you have any more questions then please let us know.
Cambridge Open Systems Support Team