public IActionResult ExternalLogin(string provider, string returnUrl = null)
{
string redirectUrl;
// Request a redirect to the external login provider.
redirectUrl = $"Account/{nameof(ExternalLoginCallback)}/";//Url.Action(nameof(ExternalLoginCallback), "Account", new { returnUrl });
AuthenticationProperties properties = _authentication.ConfigureExternalAuthenticationProperties(provider, redirectUrl);
return(Challenge(properties, provider));
}