TelegramAuthValidation.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace Campus.Core.Social
{
	public class TelegramAuthResponse
	{
		public int auth_date { get; set; }
		public string first_name { get; set; }
		public string hash { get; set; }
		public int id { get; set; }
		public string photo_url { get; set; }
		public string username { get; set; }
	}

	public class TelegramClient
	{
		private readonly string _botKey;

		public TelegramClient(string botKey)
		{
			_botKey = botKey;
		}

		public bool CheckTelegramAuthorization(TelegramAuthResponse response)
		{
			var checkList = new List<string>
			{
				$"auth_date={response.auth_date}",
				$"first_name={response.first_name}",
				$"id={response.id}",
				$"photo_url={response.photo_url}",
				$"username={response.username}"
			};

			checkList.Sort();

			var dataCheckString = string.Join("\n", checkList);

			var secretKey = HashString(_botKey);
			var hash = GetHashSha256(secretKey, dataCheckString);

			return response.hash == hash;
		}

		private static byte[] HashString(string text) => 
			new SHA256Managed().ComputeHash(Encoding.UTF8.GetBytes(text));
		
		

		public static string GetHashSha256(byte[] secretKey, string text)
		{
			var hash = new HMACSHA256(secretKey).ComputeHash(Encoding.UTF8.GetBytes(text));
			return hash.Aggregate(string.Empty, (current, x) => current + $"{x:x2}");
		}
	}
}