public async Task <IActionResult> Token(
string grant_type,
string code,
string redirect_uri,
string client_id)
{
UserToken userToken = await _userTokenRepository.GetAsync(code);
if (userToken is null || userToken.IsCanceled || redirect_uri != userToken.RedirectUri)
{
return(BadRequest(new { error = "invalid_request" }));
}