yaflay.ru/Pages/Authorize.cshtml

@page "{code}"
@model yaflay.ru.Pages.AuthorizeModel
@using System.Text.Json.Nodes
@{
    ViewData["Title"] = "Authorize";
    if (Model.code == null)
    {
        if (Request.Cookies["melon"]?.ToString() == null)
        {
            <a href="https://discord.com/api/oauth2/authorize?client_id=1115013432710799440&response_type=code&redirect_uri=https%3A%2F%2Fyawaflua.ru%2Fauthorize&scope=identify">Login while Discord</a>
        }
        else
        {
            HttpResponseMessage message;
            using (var requestMessage =
                new HttpRequestMessage(HttpMethod.Get, "https://discordapp.com/api/oauth2/@me"))
            {
                requestMessage.Headers.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Bearer", Request.Cookies["melon"]); ;
                message = await Startup.client.SendAsync(requestMessage);
            }
            string responseBody = await message.Content.ReadAsStringAsync();
            JsonNode response = JsonNode.Parse(responseBody);
            if (response["user"] != null)
            {
                <h4>Вы авторизованы!</h4>
                <a href="/AdminPanel"> Админка </a>
            }
            else
            {
                <h4>
                    Токен авторизации неправильный! Попробуйте <a href="https://discord.com/api/oauth2/authorize?client_id=1115013432710799440&response_type=code&redirect_uri=https%3A%2F%2Fyawaflua.ru%2Fauthorize&scope=identify">заново</a>
                </h4>
            }

        }
    }
    else
    {

        HttpResponseMessage message;
        using (var requestMessage =
            new HttpRequestMessage(HttpMethod.Post, "https://discordapp.com/api/oauth2/token"))
        {
            requestMessage.Content = new StringContent(
                @$"grant_type=authorization_code&code={Model.code}&client_id={Startup.clientId}&client_secret={Startup.clientSecret}&scope=identify&redirect_uri={Startup.redirectUrl}", 
                new System.Net.Http.Headers.MediaTypeHeaderValue("application/x-www-form-urlencoded")
                );
            message = await Startup.client.SendAsync(requestMessage);
        }
        string responseBody = await message.Content.ReadAsStringAsync();
        JsonNode body = JsonNode.Parse(responseBody);
        if (body["access_token"]?.ToString() == null)
        {
            <h4>Ошибка! Попробуй авторизоваться заново</h4>
        }
        else
        {
            Response.Cookies.Append("melon", body["access_token"].ToString());
            Response.Cookies.Append("watermelon", body["refresh_token"].ToString());
            Response.Redirect("/authorize");
        }
    }
}