Access Denied with Custom Credentials

[Homa]

Hi all,
I'm exploring how to make authentication works with WebService.

I've setup the WebService with no anonymous access and using
Integrated Windows authentication.

In my web-app or win-app, if I set the Credentials to
System.Net.CredentialCache.DefaultCredentials, it runs fine.

But since I want to identify my caller, I try to do the following:

<code>
(using System.Net

CredentialCache cache = new CredentialCache();
cache.Add(new Uri(myWebServiceProxy.Url), "Negotiate",
new NetworkCredential("myUsername", "myPassword"));
myWebServiceProxy.Credentials = cache;
</code>


And now I get Access Denied.
I tried to use admin's username/password, ASPNET/myStrongPassword.

Am I doing it the right way? What have I missed?

Information:
In machine.config, I set processModel with username="machine",
password="myStrongPassword"

When I look at the debugger, the DefaultCredentials contains the
SystemNetworkCredential with username/password/domain == "" (m_xxx =
undefined).



I'm trying to follow the suggestion from the book "Building Secure
Microsoft ASP.NET Applications - Authenticaion, Authorization, and
Secure Communication -- patters & practices" from Microsoft Press,
page 240.

Thanks for concern,
Homa Wong