How to Supply Credentials to a Web Service

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When an web services is secured with Windows Authentication and you need to call it as a specific user or another account on the domain, this article explains how to do it.

https://support.microsoft.com/default.aspx?scid=kb;en-us;813834 

You can either set the proxy class's Credentials = to System.Net.CredentialCache.DefaultCredentials or supply an alternative set of credentials to the proxy class's Credentials policy.