ASP.NET web service permissions reading file system using machine account

I have a web application that runs on SERVER_A. The web application calls a web service which runs on SERVER_B. The web service returns a set of folder names on the file system from SERVER_B. However the web service fails to return any content when I run my application from SERVER_A, but it works OK when I access the web service directly via a browser or my localhost i.e. via Visual Studio. I can get it to开发者_StackOverflow中文版 work for SERVER_A if I grant the machine name (SERVER_A) access to the file system via Properties > Security. But I don't think this is very secure..?

Ideally I need to grant a service account the correct permissions, but how do I do this? Do I need to run my application on SERVER_A as this service account in order for it pass the identity when it connects to my web service? If so how do I do this?

You can specify the credientials you are using with the webservice. Once you create your service account (if you haven't already) you can specify the credentials when trying to consume the webservice...here is a MS kb article (take a look at the "Second Method").

http://support.microsoft.com/kb/811318