Release SharePoint document lock through server side code (C#)

Release-File.cs

SPList list = web.Lists[txtListTitle.Text];
SPListItem item = list.GetItemById(int.Parse(txtItemID.Text));
SPFile file = item.File;
if (file.LockType == SPFile.SPLockType.None)
{
    txtOutput.Text = "File is not locked";
}
else
{
    int lockUserID = file.LockedByUser.ID;
    string lockId = file.LockId;
    SPUser user = web.AllUsers.GetByID(lockUserID);
    try
    {
        web.AllowUnsafeUpdates = true;
        //no one but the user him/herself can release an exclusive lock
        //http://blog.aspjava.com/2016/06/sharepoint-unlock-file-that-is.html
        using (SPSite userSite = new SPSite(txtWebUrl.Text, user.UserToken))
        {
            using (SPWeb userWeb = userSite.OpenWeb())
            {
                SPList userList = userWeb.Lists[txtListTitle.Text];
                SPListItem userItem = userList.GetItemById(int.Parse(txtItemID.Text));
                SPFile userFile = userItem.File;

                userWeb.AllowUnsafeUpdates = true;
                userFile.ReleaseLock(lockId);
            }
        }
        txtOutput.Text = "Lock released!";
    }
    catch (Exception ex)
    {
        txtOutput.Text = "Error: " + ex.Message;
    }
    finally
    {
        web.AllowUnsafeUpdates = false;
    }
}