还有其他选项可以实现“HttpContext.GetServiceProviders（）”＆amp; “Http.Context.IsProviderSupported（供应商）”？

Question

 public class AuthenticationController : Controller
    {
        [HttpGet("~/signin")]
        public IActionResult SignIn() => View("SignIn", HttpContext.GetExternalProviders());
        [HttpPost("~/signin")]
        public IActionResult SignIn([FromForm] string provider)
        {
            // Note: the "provider" parameter corresponds to the external
            // authentication provider choosen by the user agent.
            if (string.IsNullOrWhiteSpace(provider))
            {
                return BadRequest();
            }

            if (!HttpContext.IsProviderSupported(provider))
            {
                return BadRequest();
            }

            // Instruct the middleware corresponding to the requested external identity
            // provider to redirect the user agent to its own authorization endpoint.
            // Note: the authenticationScheme parameter must match the value configured in Startup.cs
            return Challenge(new AuthenticationProperties { RedirectUri = "/" }, provider);
        }

        [HttpGet("~/signout"), HttpPost("~/signout")]
        public IActionResult SignOut()
        {
            // Instruct the cookies middleware to delete the local cookie created
            // when the user agent is redirected from the external identity provider
            // after a successful authentication flow (e.g Google or Facebook).
            return SignOut(new AuthenticationProperties { RedirectUri = "/" },
               SalesforceAuthenticationDefaults.AuthenticationScheme);
        }
    }

(!HttpContext.IsProviderSupported(provider)) & HttpContext.GetExternalProviders() - 在Visual Studio 2017中生成错误，但它在Visual Studio代码

中有效

我不确定为什么这样做，但对这些问题的任何帮助都非常感谢。