OAuthController.cs

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using PixelNetwork.Properties;

namespace PixelNetwork.Controllers
{
    /// <summary>
    /// OAuthController should be deployed as a part of your ASP.NET website.
    /// It may contain insignificant dependencies to other parts of the original Authorization Middleware, just comment or replace them.
    /// Alternatively, you can use it as a reference and implement the same logic with other programming languages and platforms.
    /// </summary>
    [Route("api/[controller]")]
    public class OAuthController : ControllerBase
    {
        private static readonly OrderedDictionary Redirects = new OrderedDictionary();
        private static readonly OrderedDictionary Codes = new OrderedDictionary();

        [HttpPost("init")]
        public void Init(string state, string redirectUri, string clientName)
        {
            if (state == null || (state.Length != 32 && state.Length != 36)) throw new Exception("Invalid state.");

            lock (Redirects)
            {
                if (Redirects.Count >= 1000) for (var i = 0; i < 100; i++) Redirects.RemoveAt(0);
                if (Redirects.Contains(state)) Redirects.Remove(state);

                Redirects.Add(state, redirectUri);
            }
        }

        [HttpGet("redirect")]
        public IActionResult Redirect(string code, string state)
        {
            if (code == null || state == null) throw new Exception("Invalid parameters.");

            lock (Redirects)
            lock (Codes)
            {
                if (!Redirects.Contains(state)) throw new Exception("Unexpected state.");
                if (Codes.Count >= 1000) for (var i = 0; i < 100; i++) Codes.RemoveAt(0);
                if (Codes.Contains(state)) Codes.Remove(state);

                var redirectUri = (string) Redirects[state];

                Redirects.Remove(state);

                if (string.IsNullOrEmpty(redirectUri))
                {
                    Codes.Add(state, code);
                }
                else
                {
                    Response.Redirect($"{redirectUri}?code={code}&state={state}", permanent: true);
                }
            }

            var template = Request.Headers.TryGetValue("Referer", out var referer) && (referer.Contains("https://id.vk.com/") || referer.Contains("https://twitter.com/") || referer.Contains("/telegramwidget") || referer.Contains("https://appleid.apple.com/") || referer.Contains("https://discord.com/"))
                ? Resources.OAuthTemplate
                : Resources.OAuthTemplateAutoClosed;

            if (Request.GetDisplayUrl().Contains("platform=telegram"))
            {
                template = Resources.OAuthTemplate;
            }

            return Content(template, "text/html", Encoding.UTF8);
        }

        [HttpPost("get_code"), HttpPost("getcode")]
        public IActionResult GetCode(string state)
        {
            if (state == null) throw new Exception("Invalid parameters.");

            lock (Codes)
            {
                if (!Codes.Contains(state)) return StatusCode(704);

                var code = (string) Codes[state];

                Codes.Remove(state);

                return Content(code);
            }
        }

        [HttpPost("download")]
        public async Task<string> Download(string url, string form)
        {
            var allowed = new List<string>
            {
                "https://appleid.apple.com/auth/token", "https://appleid.apple.com/auth/revoke",
                "https://api.twitter.com/2/oauth2/token", "https://api.twitter.com/2/oauth2/revoke", "https://api.twitter.com/2/users/me",
                "https://open.tiktokapis.com/v2/oauth/token/", "https://open.tiktokapis.com/v2/oauth/revoke/",
                "https://oauth.vk.com/access_token", "https://api.vk.com/method/users.get"
            };

            if (!allowed.Any(url.StartsWith)) throw new Exception("Unsupported url.");

            using var client = new HttpClient();

            if (Request.Headers.TryGetValue("Authorization", out var authorization) && authorization.Count == 1)
            {
                client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(authorization[0].Split(' ')[0], authorization[0].Split(' ')[1]);
            }

            if (form == null) return await client.GetStringAsync(url);

            var dict = JsonConvert.DeserializeObject<Dictionary<string, string>>(form);
            var content = new FormUrlEncodedContent(dict);
            var response = await client.PostAsync(url, content).Result.Content.ReadAsStringAsync();
            
            return response;
        }

        [HttpPost("apple_redirect")]
        public IActionResult AppleRedirect(string code, string id_token, string state, string user)
        {
            if (code == null || state == null) throw new Exception("Invalid parameters.");

            code = Convert.ToBase64String(Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(new { code, user = user == null ? null : JObject.Parse(user) })));

            return Redirect(code, state);
        }

        [HttpGet("telegram_auth")]
        public IActionResult TelegramAuth(string id, string state, int widget)
        {
            var html = widget == 1
                ? "<html><body><div style='display: flex; justify-content: center; align-items: center; height: 200px;'><script async src='https://telegram.org/js/telegram-widget.js?22' data-telegram-login='{id}' data-size='large' data-onauth='onTelegramAuth(user)' data-request-access='write'></script><script type='text/javascript'>function onTelegramAuth(user) { location.href='https://hippogames.dev/api/oauth/redirect?platform=telegram&state={state}&code=' + btoa(JSON.stringify(user)); }</script></div></body></html>"
                : "<html><body><script src='https://telegram.org/js/telegram-widget.js'></script><script>window.Telegram.Login.auth({ bot_id: '{id}', request_access: true }, (data) => { window.location.href = 'https://hippogames.dev/api/oauth/redirect?platform=telegram&state={state}&code=' + btoa(JSON.stringify(data)); });</script></body></html>";

            html = html.Replace("{id}", id);
            html = html.Replace("{state}", state);

            return Content(html, "text/html", Encoding.UTF8);
        }
    }
}