YouTubeScraper/YouTube.API/Authorization/AuthorizationHelpers.cs

using Google.Apis.Auth.OAuth2;
using Google.Apis.Auth.OAuth2.Flows;
using Google.Apis.Auth.OAuth2.Responses;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace YouTube.Authorization
{
	public static class AuthorizationHelpers
	{
		public static Uri Endpoint => "https://accounts.google.com/o/oauth2/approval".ToUri();
		private const string refreshEndpoint = "https://oauth2.googleapis.com/token";
		private const string tokenEndpoint = "https://www.googleapis.com/oauth2/v4/token";
		private const string redirectUrl = "urn:ietf:wg:oauth:2.0:oob";

		public static Uri FormQueryString(ClientSecrets clientSecrets, params string[] scopes)
		{
			string clientId = Uri.EscapeDataString(clientSecrets.ClientId);
			string scopeStr = string.Join(" ", scopes);

			return $"https://accounts.google.com/o/oauth2/auth?client_id={clientId}&redirect_uri={redirectUrl}&response_type=code&scope={scopeStr}".ToUri();
		}

		public static string ParseSuccessCode(string responseData) =>
			new Regex(@"(?<=code=)(.*?)(?=&)").Match(responseData).Value;

		public static async Task<UserCredential> ExchangeToken(ClientSecrets clientSecrets, string responseToken)
		{
			using HttpClient client = new HttpClient();

			Dictionary<string, string> requestBody = new Dictionary<string, string>
			{
				{ "code", responseToken },
				{ "redirect_uri", redirectUrl },
				{ "grant_type", "authorization_code" },
				{ "client_id", clientSecrets.ClientId },
				{ "client_secret", clientSecrets.ClientSecret }
			};

			HttpResponseMessage response = await client.PostAsync(tokenEndpoint, new FormUrlEncodedContent(requestBody));

			if (!response.IsSuccessStatusCode)
				throw new Exception(await response.Content.ReadAsStringAsync());

			string responseString = await response.Content.ReadAsStringAsync();
			dynamic responseData = JsonConvert.DeserializeObject(responseString);

			TokenResponse tokenResponse = new TokenResponse
			{
				AccessToken = responseData.access_token,
				ExpiresInSeconds = responseData.expires_in,
				RefreshToken = responseData.refresh_token,
				Scope = responseData.scope,
				TokenType = responseData.token_type
			};

			AuthorizationCodeFlow authorizationCodeFlow = new GoogleAuthorizationCodeFlow(new GoogleAuthorizationCodeFlow.Initializer
			{
				ClientSecrets = clientSecrets,
				Scopes = responseData.scope.ToString().Split(' ')
			});

			UserCredential credential = new UserCredential(authorizationCodeFlow, "user", tokenResponse);

			return credential;
		}

		public static async Task<UserCredential> RestoreUser(ClientSecrets clientSecrets, string refreshToken)
		{
			using HttpClient client = new HttpClient();

			Dictionary<string, string> requestBody = new Dictionary<string, string>
			{
				{ "client_id", clientSecrets.ClientId },
				{ "client_secret", clientSecrets.ClientSecret },
				{ "refresh_token", refreshToken },
				{ "grant_type", "refresh_token" }
			};

			HttpResponseMessage response = await client.PostAsync(refreshEndpoint, new FormUrlEncodedContent(requestBody));

			if (!response.IsSuccessStatusCode)
				throw new Exception(await response.Content.ReadAsStringAsync());

			string responseString = await response.Content.ReadAsStringAsync();
			dynamic responseData = JsonConvert.DeserializeObject(responseString);

			TokenResponse tokenResponse = new TokenResponse
			{
				AccessToken = responseData.access_token,
				ExpiresInSeconds = responseData.expires_in,
				RefreshToken = refreshToken,
				TokenType = responseData.token_type
			};

			AuthorizationCodeFlow authorizationCodeFlow = new GoogleAuthorizationCodeFlow(new GoogleAuthorizationCodeFlow.Initializer
			{
				ClientSecrets = clientSecrets
			});

			UserCredential credential = new UserCredential(authorizationCodeFlow, "user", tokenResponse);

			return credential;
		}
	}
}