JWT Decoder

 JWT Decoder Uncaught Error: Cannot pass parameter 3 by reference

It appears that the issue might be coming from how the JWT::decode method is being called. The JWT::decode function from the Firebase PHP JWT library does not take parameters by reference, so this error is unexpected unless another part of your code is involved. Let's troubleshoot and rewrite the code with alternative error handling in case there's some hidden behavior or server configuration affecting this.

The error you're encountering, "Cannot pass parameter 3 by reference", occurs because the JWT::decode function in the Firebase JWT library has been updated, and it now requires a slightly different syntax.

In recent versions, the JWT::decode method expects the $key (the second parameter) to be passed as an array when specifying the algorithm, instead of a separate array for algorithms as the third parameter. Here’s how to modify the line:

New Approach

$decoded = JWT::decode($jwt, new \Firebase\JWT\Key($secret_key, 'HS256'));

Old Approach

$decoded = JWT::decode($jwt, $secret_key, ['HS256']); 

To debug by echoing the JWT and secret key in your PHP script, you can add echo statements right before the JWT::decode method.

Here is Complete Example

<?php

include_once($_SERVER['DOCUMENT_ROOT'] . "/header.php");

require __DIR__ . '/vendor/autoload.php';

use \Firebase\JWT\JWT;

ini_set('display_errors', 1);

ini_set('display_startup_errors', 1);

error_reporting(E_ALL);

$secret_key = "Your key";

// Fetch headers safely

$headers = apache_request_headers();

if (isset($headers['Authorization'])) {

    // Remove "Bearer " from the token string

    $jwt = str_replace("Bearer ", "", $headers['Authorization']);

    // Debug output for JWT and secret key

    echo "JWT Token: " . htmlspecialchars($jwt) . "<br>";

    echo "Secret Key: " . htmlspecialchars($secret_key) . "<br>";

    try {

        // Decode JWT

        $decoded = JWT::decode($jwt, $secret_key, ['HS256']);

        

        // Success response

        echo json_encode(["status" => 200, "message" => "Access granted", "data" => $decoded]);

    } catch (\Firebase\JWT\ExpiredException $e) {

        echo json_encode(["status" => 401, "message" => "Token expired", "error" => $e->getMessage()]);

    } catch (\Firebase\JWT\SignatureInvalidException $e) {

        echo json_encode(["status" => 401, "message" => "Invalid signature", "error" => $e->getMessage()]);

    } catch (Exception $e) {

        // General error response for other exceptions

        echo json_encode(["status" => 401, "message" => "Access denied", "error" => $e->getMessage()]);

    }

} else {

    // Missing token response

    echo json_encode(["status" => 401, "message" => "Token not provided"]);

}

?>

Explanation:

1. Echo JWT: The htmlspecialchars($jwt) is used to safely display the token, which can help prevent any unintended HTML injection if the JWT contains special characters.

2. Echo Secret Key: Similarly, the htmlspecialchars($secret_key) is used to safely display the secret key.

3. Important Reminder: Remove or comment out these echo statements once you’ve completed debugging to avoid exposing sensitive information.

The error "Class 'Key' not found" means that PHP couldn’t locate the Key class from the Firebase JWT library. This issue usually happens if the library version is not up-to-date or if the namespace for Key is missing.

1. Check Firebase JWT Library Version: First, ensure you have the latest version of the Firebase JWT library installed (version 5.0 or newer), as the Key class was introduced in that version. You can check your composer.json file to confirm.

2. Add Correct Namespace: In your script, ensure you’re using the full namespace for Key (\Firebase\JWT\Key).

3. Install or Update the Firebase JWT Library: Run the following command in your project’s root directory to update to the latest version:

Testing in the Browser or Postman

When you access this endpoint from a browser or use Postman to make the request, you should see the JWT token and secret key echoed on the screen if the Authorization header is provided. 

Namespace for Key: use \Firebase\JWT\Key; includes the Key class.

Decoding with Key: JWT::decode($jwt, new Key($secret_key, 'HS256')); is used to decode the token securely.

If there are issues with the token, this output will help verify that the values are being received and parsed correctly.