Facebook Authorization (Facebook Login) And Access [Code] Querystring Parameter Value

Facebook authorization (Facebook login) and access [code] querystring parameter value using Facebook nuget package in C# applications.

Facebook authorization (facebook login) and access [code] querystring parameter value using facebook nuget package in C# application.

1. Need to install "facebook" nuget package in c# project.
2. Must create your Facebook app from https://developers.facebook.com/ and store appId and appSecret in your application.
3. Execute below code for facebook authorization and call "FacebookLogin" method on action event. fig-1
   

   //fig-1
   [HttpPost]
   public string FacebookLogin() {
       try {
           // Instantiate the Facebook client
           var oauth = new FacebookClient();
           var fbLoginUrl = oauth.GetLoginUrl(new {
               client_id = "Enter ApplicationID",
                   client_secret = "Enter ApplicationSecret",
                   redirect_uri = "Enter RedirectUri",
                   response_type = "code",
                   scope = "manage_pages,email" // Add other permissions as needed
           });
           var fbloginUri = fbLoginUrl.AbsoluteUri;
           Session["ClientId"] = "Enter ApplicationID",
               return fbloginUri;
       } catch (Exception) {
           return null;
       }
   } // This is just a sample script. Paste your real code (javascript or HTML) here.
   if ('this_is' == /an_example/) {
       of_beautifier();
   } else {
       var a = b ? (c % d) : e[f];
   }

4. Here, you get below url for facebook login page,
   
   https://www.facebook.com/login.php?skip_api_login=?&api_key=?&signed_next=?&next=?&cancel_url=?&display=?&locale=?&logger_id=?
   
   
5. After authoriing Facebook user, you get below url with [code] querystrings parameter:
   
   http://localhost:url?code=?
   
   
6. You need to store [code] query string parameter value in session and call below function in page_load event. fig-2
   

   //fig-2
   public void GetQueryStringValue() {
       string _code = string.Empty;
       if (!string.IsNullOrEmpty(System.Web.HttpContext.Current.Request.UrlReferrer.Query)) {
           List < string > collection = GetQueryStringCollection(System.Web.HttpContext.Current.Request.UrlReferrer.Query, 0);
           if (collection != null && collection.Count > 0) {
               _code = System.Web.HttpContext.Current.Server.UrlDecode(collection[0]);
               Session["code"] = _code;
           }
       }
   }
   // Get Querystring name value collection
   public List < string > GetQueryStringCollection(string url, int count) {
       string keyValue = string.Empty;
       List < string > collection = new List < string > ();
       string[] querystrings = url.Split('&');
       if (querystrings != null && querystrings.Count() > count) {
           for (int i = 0; i < querystrings.Count(); i++) {
               string[] pair = querystrings[i].Split('=');
               collection.Add(pair[1]);
           }
       }
       return collection;
   }