冒充用户名和密码？

WindowsIdentity identity = new WindowsIdentity(accessToken);
WindowsImpersonationContext context = identity.Impersonate();

 ...
context.Undo();

在哪里声明管理员用户名和密码？

the 访问令牌param 对我没有太大帮助......

我必须为其导入 DLL 吗？

您需要获取用户的令牌。使用 p/调用LogonUser来自 advapi32.dll：

    [DllImport("advapi32.dll", SetLastError = true)]
    public static extern bool LogonUser(
            string lpszUsername,
            string lpszDomain,
            string lpszPassword,
            int dwLogonType,
            int dwLogonProvider,
            out IntPtr phToken);

Example:

IntPtr userToken = IntPtr.Zero;

bool success = External.LogonUser(
  "john.doe", 
  "domain.com", 
  "MyPassword", 
  (int) AdvApi32Utility.LogonType.LOGON32_LOGON_INTERACTIVE, //2
  (int) AdvApi32Utility.LogonProvider.LOGON32_PROVIDER_DEFAULT, //0
  out userToken);

if (!success)
{
  throw new SecurityException("Logon user failed");
}

using (WindowsIdentity.Impersonate(userToken))
{
  // do the stuff with john.doe's credentials
}