Moodle Authentication Using an External Web Service

Hi, Folks,

I have an external web service for authentication in my company and I'd like to connect Moodle with it, but I'm not being able to do it.

When I activate the web service authentication plugin, I see the message that I cannot use it exclusively with web accounts. 

Maybe it's a newbie or stupid question, but I didn't understand why... can y ou explain it?

Thanks,

Luiz