public async Task CookiesLoginGet()
{
await HttpContext.Response.WriteHtmlAsync(async res =>
{
await res.WriteAsync($"<form method=\"post\">");
await res.WriteAsync($"<input type=\"hidden\" name=\"returnUrl\" value=\"{HttpResponseExtensions.HtmlEncode(HttpContext.Request.Query["ReturnUrl"])}\"/>");
await res.WriteAsync($"<div class=\"form-group\"><label>用户名：<input type=\"text\" name=\"userName\" class=\"form-control\"></label></div>");
await res.WriteAsync($"<div class=\"form-group\"><label>密码：<input type=\"password\" name=\"password\" class=\"form-control\"></label></div>");
await res.WriteAsync($"<button type=\"submit\" class=\"btn btn-default\">登录</button>");
await res.WriteAsync($"</form>");
});
}