public override async Task AuthenticateExternalAsync(ExternalAuthenticationContext ctx)
{
var externalUser = ctx.ExternalIdentity;
var message = ctx.SignInMessage;
if (externalUser == null)
{
throw new ArgumentNullException("externalUser");
}
var user = await _userManager.FindByLoginAsync(externalUser.Provider, externalUser.ProviderId).ConfigureAwait(false);
if (user == null)
{
ctx.AuthenticateResult = await ProcessNewExternalAccountAsync(externalUser.Provider, externalUser.ProviderId, externalUser.Claims);
}
else
{
ctx.AuthenticateResult = await ProcessExistingExternalAccountAsync(user, externalUser.Provider, externalUser.ProviderId, externalUser.Claims);
}
}