Secure JSON Web Tokens with PHP & Firebase

Question

I am using Firebase Token Generator to generate secure tokens in PHP:

const DEFAULT_SECRET = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';

date_default_timezone_set('Europe/London');

try {
    $generator = new TokenGenerator(DEFAULT_SECRET);
    $token = $generator
        ->setOptions(array(
            'expires' => strtotime('now + 1 minute'),
            'debug' => true
        ))
        ->setData(array('uid' => 'exampleID'))
        ->create();
} catch (TokenException $e) {
    echo "Error: ".$e->getMessage();
}

$response = array(
   'token' => $token
);

echo json_encode($response);

On the client side I am using a JSON request to retrieve the token as a JSON object:

 $.getJSON('http://localhost/firebase/index.php', function(json) {
        var jwtToken = json.token;
        launchFirebase(jwtToken);
 });

  function launchFirebase(token) {
      var fb = new Firebase(FirebaseURL);

      fb.authWithCustomToken(token, function(error, authData) {
        if (error) {
          alert("There was an error posting your vote. Please try again later."); 
        } else {
          checkEmail();
        }
      });

      function checkEmail(){
        new Firebase(FirebaseURL)
          .orderByChild('email')
          .startAt(vote.email)
          .endAt(vote.email)
          .once('value', function(snap) {
             var result = snap.val();
             callback(result);
        });
      } 
  }

I can now read data from Firebase so this works fine. My security concern is that anyone can view the source code and go directly to the PHP script (http://localhost/firebase/index.php) to retrieve the token.

They could then view all the data via an API call like this: https://examplesite.firebaseio.com/.json?print=pretty&auth=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

What's the best practice to keep the PHP script secure?

londonfed · Accepted Answer · 2016-05-23 09:55:48Z

I figured out that I needed to move the client logic inside my server side script so it is secure. I am now using Firebase PHP Client.

Inside my PHP script I have:

const DEFAULT_URL = 'https://examplesite.firebaseio.com/';
const DEFAULT_TOKEN = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';
const DEFAULT_PATH = '/';

$firebase = new \Firebase\FirebaseLib(DEFAULT_URL, DEFAULT_TOKEN);

// --- reading the Firebase database ---
$database = $firebase->get(DEFAULT_PATH);

$searchString = $_GET["email"]; 

if (strpos($database,$searchString) !== false) {
    $response = array(
        'emailExists' => true
    );
} else {
    $response = array(
        'emailExists' => false
    );
}

echo json_encode($response);

And then on the client side I have:

findUser: function(email, callback){

  $.getJSON('https://PHP_LOCATION.com/index.php', {
    email: email
  }, function(json) {
        callback(json.emailExists);
  });

}

For info': the purpose of this script is to check whether or not an email address already exists in the Firebase database.

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