Is it possible to call a c# WebService with current windows user credentials? (SharePoint)

Is it possible to call a c# WebService with current windows user
credentials? (SharePoint)

I have a small C# ASP.Net WebService. I like to call this WebService from
a windows Client and do some things on a SharePoint Document Library.
(e.g. uploading a file)
But if I upload a file it will be executed with the credentials from the
webservice instead of the credentials from the User who invoked the
WebService. Result = All files will be displayed as "created by" = System
Account...
Is it possible to call this WebService (from browser or Script $.Ajax)
with the current Windows User Credentials and to work with these
credentials in the WebService?
I know that I can display the user who invoked the WebService for example
in this way:
return Username = User.Identity.Name;
But you can not use it to work with these type of credentials?
I already tried several things but I was not able to get the current User.
Code Example1: (SharePoint Client Object Model)
ClientContext context = new ClientContext("http://intranet.harter.local");
context.Credentials = System.Net.CredentialCache.DefaultCredentials;
Code Example2: (SharePoint Server Object Model)
SPUserToken userToken = null;
SPSecurity.RunWithElevatedPrivileges(delegate()
{
using (SPSite site = new SPSite("SiteUrl"))
{
using (SPWeb web = site.OpenWeb())
{
userToken = web.AllUsers["DOMAIN\\USERNAME"].UserToken;
}
});
using (SPSite site = new SPSite("SiteUrl", userToken))
{
using (SPWeb web = site.OpenWeb())
{
// Perform actions
}
}
Code Example3: (I don´t like that one) I found one possible way but I have
to type the password plain in code what I don´t like:
NetworkCredential credentials = new NetworkCredential("username", "pwd",
"domain");
ClientContext context = new ClientContext("http://site-url");
context.Credentials = credentials;
...
I think the most important things in the web.config file are also here?:
<authentication mode="Windows"/>
<add name="Access-Control-Allow-Origin" value="http://domain.local"/>
<add name="Access-Control-Allow-Credentials" value="true"/>
<add name="Access-Control-Allow-Headers" value="Content-Type"/>
Any ideas how I can execute the Code with the user context from the
current user?