code: func (c *ServerContext) GetUsername() (string, error) {
  	var ns _SecPkgContext_NativeNames
  	ret := sspi.QueryContextAttributes(c.sctxt.Handle, _SECPKG_ATTR_NATIVE_NAMES, (*byte)(unsafe.Pointer(&ns)))
  	if ret != sspi.SEC_E_OK {
  		return "", ret
  	}
  	sspi.FreeContextBuffer((*byte)(unsafe.Pointer(ns.ServerName)))
  	defer sspi.FreeContextBuffer((*byte)(unsafe.Pointer(ns.ClientName)))
  	return syscall.UTF16ToString((*[2 << 20]uint16)(unsafe.Pointer(ns.ClientName))[:]), nil
  }
docs: // GetUsername returns the username corresponding to the authenticated client