How to get Windows user name when identity impersonate="true" in asp.net?

With <authentication mode="Windows"/> in your application and Anonymous access enabled in IIS, you will see the following results:

System.Environment.UserName: Computer Name
Page.User.Identity.Name: Blank
System.Security.Principal.WindowsIdentity.GetCurrent().Name: Computer Name 

With <authentication mode="Windows"/> in your application, and ‘Anonymous access’ disabled and only ‘Integrated Windows Authentication’ in IIS, you will see the following results:

System.Environment.UserName: ASPNET (user account used to run ASP.NET service)
Page.User.Identity.Name: Domain\ Windows Account Name 
System.Security.Principal.WindowsIdentity.GetCurrent().Name: Computer Name\ASPNET

With <authentication mode="Windows"/> and <identity impersonate ="true"/> in your application, and ‘Anonymous access’ disabled and only ‘Integrated Windows Authentication’ in IIS, you will see the following results:

System.Environment.UserName: Windows Account Name 
Page.User.Identity.Name: Domain\ Windows Account Name 
System.Security.Principal.WindowsIdentity.GetCurrent().Name: Domain\ Windows Account Name

try this

System.Security.Principal.WindowsIdentity.GetCurrent().Name

It should return a string with the users login name