[1]

   1:  WS.Credentials = new System.Net.NetworkCredential(userName, password, domain);

If you want to pass explicit credentials and filter the record after that.

 

[2]

http://support.microsoft.com/kb/813834

   1:  myProxy.Credentials = System.Net.CredentialCache.DefaultCredentials

It will pick up the current logged in users’ credentials and return the data for him/her.

 

[3]

Using SharePoint object model, setting up our custom web service on SharePoint box and access it.

   1:              SPUser spUser = null;
   2:              string authError = "Could not authenticate user";
   3:              try
   4:              {
   5:                  spUser = web.AllUsers[impUser];
   6:                  if (spUser == null)
   7:                  {
   8:                      writer.Write(string.Format("spUser = web.AllUsers[impUser]; failed<br/>"));
   9:                      throw new UnauthorizedAccessException(authError);
  10:                  }
  11:              }
  12:   
  13:                  SPUserToken token = spUser.UserToken;
  14:              using (SPSite impSite = new SPSite(SPContext.Current.Site.ID, token))
  15:              {
  16:                  impSite.CatchAccessDeniedException = false;
  17:                  using (SPWeb impWeb = impSite.OpenWeb(SPContext.Current.Web.ID))
  18:                  {
  19:                      writer.Write(string.Format("Success with impersonated site context. {0}:<br/>", impWeb.CurrentUser.LoginName));
  20:                      SPList list = null;
  21:                      
  22:                      try
  23:                      {
  24:                          list = web.Lists[this.ListName];
  25:                      }
  26:                      catch (ArgumentException ex)
  27:                      {
  28:                          writer.Write(string.Format("Couldn't access list web.Lists[this.ListName]<br/>"));
  29:                          writer.Write(ex.ToString());
  30:                          writer.Write(string.Format("<br/>"));    
  31:                      }
  32:   
  33:                      try
  34:                      {
  35:                          list.CheckPermissions(SPBasePermissions.ViewListItems);
  36:                          context.Response.Write("<p>OK! :) Succesfully checked permissions.</p>");
  37:                      }
  38:                      catch(Exception ex)
  39:                      {
  40:                          context.Response.Write("Security check failed.<br/>");
  41:                          context.Response.Write(string.Format("Current user: {0}<br/>", list.ParentWeb.CurrentUser.LoginName));
  42:                          context.Response.Write(ex.ToString());
  43:                          context.Response.Write("<br/>");
  44:                      }
  45:                      return;
  46:                  }
  47:              }

[4]

   1:  SPSite oSite1 = new SPSite("http://eka:9001");
   2:  SPWebApplication oWebApp = oSite1.WebApplication;
   3:  SPApplicationPool oAppPool = oWebApp.ApplicationPool;
   4:              
   5:  string[] strUserIno = oAppPool.Username.Split('\\');
   6:  string strDomain = strUserIno[0].ToString();
   7:  string strUserName = strUserIno[1].ToString();
   8:  string strPassword = oAppPool.Password;