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

[djburak]

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 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?