Call a web-service under current user credentials

Question

I have a custom WCF web-service confugured with windows authentication and a WPF client application that needs to call the former. The service checks the username and pull some specific data from a database. So I have to call the service using credentials of the user running the application.

The problem is my service is hosted under another site with windows authentication and users can authenticate there with another accounts. Windows (or IE?) caches last accout used and then my client app uses it too!

Example:

I enter the website under "MYDOMAIN\AdminUser"

I run following code (from the client app, it's not web code)

var client = new TestServiceClient();
var currentUser = WindowsIdentity.GetCurrent(); // just informative field nothing more, i don't use it anyhow
// currentUser.Name = "MYDOMAIN\\MyUserName" - it's current value, i'm not trying to set it
client.ClientCredentials.Windows.ClientCredential = CredentialCache.DefaultNetworkCredentials;
var data = client.GetTestData();

Service gets called by "MYDOMAIN\AdminUser"..

I know I can create NetworkCredential with name and password but I then will have to store it somewhere, encript it and so on..

To clarify the problem: client process running under one account calls the service under another account by itself, just becouse windows supplies the call with another credentials under the hood.