In this post we will look at building a Facebook login system without using Facebook SDK. This mechanism can be followed by any website to integrate Facebook login into it. In this post we will be using a very high level abstraction to build a completely working and secure Facebook login system which will work on web apps.
We have used php for building our login system but you can use any other language as the procedure is same.
What is OAuth?
OAuth is a protocol used to allow secure authorization to websites and applications. There are two versions of OAuth, 1.0 and 2.0. In this post we will use OAuth 2.0 to build a Facebook login system.
What is Facebook Log In?
“Facebook Login In” means asking user to grant access to his/her facebook information like email id, username, friends, posts etc. Once your website has been granted access and has all these information about the user it can allow the user’s to access protected pages on your website.
Creating a Facebook App
If your website is allowing login using facebook then your website is considered as an facebook app. So you have your website ready now its time to register you website as a facebook app. Follow this steps to register your website as an facebook app:
1. Click Here to visit Facebook apps page.
2. Click on “Create New App”.
3. Enter display name as your website title. Then choose category. Finally click “Create App”.
4. Now click on App name and you will enter app dashboard.
5. In the left panel click “Settings”.
6. Now enter your website domain name in the box “App Domains”.
7. Now click on “Add Platform” and then choose “website”. Now enter your website main url and mobile url.
8. Now click “Save Changes”. You have successfully registered your website as a facebook app.
Login with Facebook Button
Now we need to create a Login button for our website. Create a anchor element and point to “https://www.facebook.com/dialog/oauth?client_id={app-id}&redirect_uri={redirect-url}&scope={required-info-permssions}”
- app-id: copy your facebook app id from app dashboard.
- redirect-url: specify the url where the user will be redirect once he accepts for facebook login.
- required-info-permissions: comma separated list of required information.
This is the code present in our live example:
index.php
Now when user clicks on the link, he will be asked by facebook to confirm access to our app. Once the user agrees or disagrees he will be directed back to our redirect url specified.
Redirect URL Page
If the user accepts information access to our app then facebook passes a one time generated code in the query parameter of the redirect url. Otherwise facebook passes a custom error message. If user accepts then facebook generates a access token using which we can access all user information. But facebook doesn’t sent it to us directly in the redirect url due to security reasons. So we need to retrieve it from facebook servers using the one time generated code and app secret string.
A user can disallow information access to our app from facebook anytime. So the access token can also be used to retrieve weather user is still allowing access or not. In this case all our requests to facebook servers will result in error message.
So in our redirect page first we will retrieve the access token. Then we will store our token in session array, which will be used by all requests to our website to check if user is logged in or not. And also retrieve user information.
This is the code present in our live example:
dialog-box-redirect.php
session_start();
if(isset($_GET["code"]))
{
$token_and_expire = file_get_contents("https://graph.facebook.com/oauth/access_token?client_id={app-id}&redirect_uri={redirect-url}&client_secret={app-secret-string}&code=" . $_GET["code"]);
parse_str($token_and_expire, $_token_and_expire_array);
if(isset($_token_and_expire_array["access_token"]))
{
$access_token = $_token_and_expire_array["access_token"];
$_SESSION['fb_access_code'] = $access_token;
header("Location: http://labs.qnimate.com/facebook-login/check.php");
}
else
{
echo "\n An error accoured!!!!! \n";
exit;
}
}
else
{
echo "\n An error accoured!!!!! \n";
}
?>
- app-id: Found in app dashboard
- redirect-url: same as passed earlier.
- app-secret-string: found in app dashboard. Don’t share this string with anyone. This string is the reason for secure login.
Back to user
Now we have stored the access token in the user session. Now this access token will be used by all our web pages to check if user is logged in or not. And also for retrieving user information. In the above redirect page we redirect the user to another page in our website if login is successful.
This is the code present in our live example.
check.php
session_start();
if(isset($_GET["logout"]))
{
if($_GET["logout"] == "true")
{
session_destroy();
echo "You are logged out of this website";
echo "<br><a href='index.php'>Click here to proceed to the sign in page</a>";
}
}
else if(isset($_SESSION["fb_access_code"]))
{
$user_information = file_get_contents("https://graph.facebook.com/me?access_token=" . $_SESSION["fb_access_code"] . "&fields=email,user_birthday");
$user_information_array = json_decode($user_information, true);
if(isset($user_information_array["email"]))
{
echo "Your email id is " . $user_information_array["email"] . " and you are logged in using facebook now !!!!";
echo "<br><a href='check.php?logout=true'>Log Out</a>";
}
else
{
echo "Please login in using facebook";
echo "<br><a href='index.php'>Click here to proceed to the sign in page</a>";
}
}
else
{
echo "Please login in using facebook";
echo "<br><a href='index.php'>Click here to proceed to the sign in page</a>";
}
?>
In the above code user can click logout to delete the access code from user session. Else the user can logout from facebook dashboard, in this case we will receive error message while making requests so we can assume user has logged out.
Conclusion
In this post we saw the secure way of retrieving user information and creating a login system using facebook graph api. Logging out facebook.com doesn’t make the access token invalid or logout from the app. For logging out from app you need to delete the cookie or disable app access from facebook dashboard. Thanks for reading.
