[程式碼範例分享] 使用Google OAuth API取得使用者資料(2023) | C#與ASP.NET

這篇只單純分享程式碼範例
所以不會有GCP設定教學

此篇適用於任何C#專案
例如ASP.NET WebForm, MVC, WebAPI等等
中間有使用到BCrypt.NET、Newtonsoft.Json
所以要先安裝Nuget套件

public class GoogleOAuth
{
    private const string GoogleAuthUrl = "https://accounts.google.com/o/oauth2/v2/auth";
    private const string GoogleTokenUrl = "https://oauth2.googleapis.com/token";
    private const string GoogleUserInfoUrl = "https://www.googleapis.com/oauth2/v3/userinfo";

    private string _clientId;     //Client ID
    private string _clientSecret; //Client Secret
    private string _redirectUrl;  //選擇Google帳號後要導回的網址，通常是用來處理登入資料
    private string _stateSecret;  //State的Secret，防止CSRF
    private string[] _scopes;

    public GoogleOAuth(string clientId, string clientSecret, string redirectUrl, string stateSecret)
    {
        this._clientId = clientId;
        this._clientSecret = clientSecret;
        this._redirectUrl = redirectUrl;
        this._stateSecret = stateSecret;
        this._scopes = new string[]
        {
            "https://www.googleapis.com/auth/userinfo.profile",
            "https://www.googleapis.com/auth/userinfo.email"
        };
    }

    /// <summary>
    /// 取得使用者驗證請求URL
    /// </summary>
    public string GetAuthUrl()
    {
        NameValueCollection colle = HttpUtility.ParseQueryString("");
        colle.Add("client_id", this._clientId);
        colle.Add("response_type", "code");
        colle.Add("redirect_uri", this._redirectUrl);
        colle.Add("state", this.GenerateHashState());
        colle.Add("scope", string.Join(' ', this._scopes));
        return $"{GoogleAuthUrl}?{colle.ToString()}";
    }

    /// <summary>
    /// 從使用者驗證的帳號Code取得存取Token
    /// </summary>
    public TokenData GetAccessToken(string authCode)
    {
        NameValueCollection colle = HttpUtility.ParseQueryString("");
        colle.Add("code", authCode);
        colle.Add("client_id", this._clientId);
        colle.Add("client_secret", this._clientSecret);
        colle.Add("grant_type", "authorization_code");
        colle.Add("redirect_uri", this._redirectUrl);
        string json = HttpRequest(
            GoogleTokenUrl,
            "POST",
            out bool isSuccess,
            colle.ToString(),
            null
        );
        return isSuccess ? JsonConvert.DeserializeObject<TokenData>(json) : null;
    }

    /// <summary>
    /// 取得使用者資訊
    /// </summary>
    public UserInfo GetUserInfo(TokenData data)
    {
        string json = HttpRequest(
            GoogleUserInfoUrl,
            "GET",
            out bool isSuccess,
            null,
            data.AccessToken
        );
        return isSuccess ? JsonConvert.DeserializeObject<UserInfo>(json) : null;
    }

    /// <summary>
    /// State驗證
    /// </summary>
    public bool StateVerify(string stateHash)
    {
        return Crypt.BCrypt.Verify(this._stateSecret, stateHash);
    }

    private string GenerateHashState()
    {
        return Crypt.BCrypt.HashPassword(this._stateSecret);
    }

    private string HttpRequest(
        string url,
        string method,
        out bool isSuccess,
        string body = null,
        string bearer = null
    )
    {
        HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(url);
        req.Method = method;
        req.ContentType = "application/x-www-form-urlencoded";
        if (bearer != null)
        {
            req.Headers.Add("Authorization", $"Bearer {bearer}");
        }
        if (body != null)
        {
            using (Stream stream = req.GetRequestStream())
            {
                byte[] bytes = Encoding.UTF8.GetBytes(body);
                stream.Write(bytes, 0, bytes.Length);
            }
        }
        string content = "";
        try
        {
            WebResponse res = req.GetResponse();
            using (Stream stream = res.GetResponseStream())
            {
                using (StreamReader reader = new StreamReader(stream))
                {
                    content = reader.ReadToEnd();
                }
            }
            isSuccess = true;
        }
        catch (WebException ex)
        {
            WebResponse res = ex.Response;
            using (Stream stream = res.GetResponseStream())
            {
                using (StreamReader reader = new StreamReader(stream))
                {
                    //to do something...
                }
            }
            isSuccess = false;
        }
        return content;
    }

    public class TokenData
    {
        [JsonProperty("access_token")]
        public string AccessToken { get; set; }

        [JsonProperty("expires_in")]
        public int ExpiresIn { get; set; }

        [JsonProperty("scope")]
        public string Scope { get; set; }

        [JsonProperty("token_type")]
        public string TokenType { get; set; }

        [JsonProperty("id_token")]
        public string IdToken { get; set; }
    }

    public class UserInfo
    {
        [JsonProperty("sub")]
        public string Id { get; set; }

        [JsonProperty("name")]
        public string Name { get; set; }

        [JsonProperty("email")]
        public string Email { get; set; }
    }
}

使用範例

GoogleOAuth google = new GoogleOAuth("id", "secret", "redirect", "state");
//取得要驗證登入的Google網址，直接向前端重定向(Redirect)即可
google.GetAuthUrl();
//驗證State是否正確
bool isSuccess = google.StateVerify(state);
//使用Code交換AccessToken
GoogleOAuth.TokenData token = google.GetAccessToken(code);
//使用AccessToken交換使用者資料
GoogleOAuth.UserInfo userInfo = google.GetUserInfo(token);
//登入驗證關卡 & 資料庫存取...

專案連結