app_client.php

<?php
    /**
     * This file processes the login request and sends back a token response
     * if successful.
     */
    $requestMethod = $_SERVER['REQUEST_METHOD'];

// retrieve the inbound parameters based on request type.
    switch($requestMethod) {
        
        case 'POST':
            $username = '';
            $password = '';
            
            if (isset($_POST['username'])) {$username = $_POST['username'];}
            if (isset($_POST['password'])) {$password = $_POST['password'];}
            
            if (($username == 'john.doe') && ($password == 'foobar')) {
                
                require_once('jwt.php');
                
                /**
                 * Create some payload data with user data we would normally retrieve from a
                 * database with users credentials. Then when the client sends back the token,
                 * this payload data is available for us to use to retrieve other data
                 * if necessary.
                 */
                $userId = 'USER123456';
                
                /**
                 * Uncomment the following line and add an appropriate date to enable the
                 * "not before" feature.
                 */
                // $nbf = strtotime('2021-01-01 00:00:01');
                
                /**
                 * Uncomment the following line and add an appropriate date and time to enable the
                 * "expire" feature.
                 */
                // $exp = strtotime('2021-01-01 00:00:01');
                
                // Get our server-side secret key from a secure location.
                $serverKey = '5f2b5cdbe5194f10b3241568fe4e2b24';
                
                // create a token
                $payloadArray = array();
                $payloadArray['userId'] = $userId;
                if (isset($nbf)) {$payloadArray['nbf'] = $nbf;}
                if (isset($exp)) {$payloadArray['exp'] = $exp;}
                $token = JWT::encode($payloadArray, $serverKey);
                
                // return to caller
                $returnArray = array('token' => $token);
                $jsonEncodedReturnArray = json_encode($returnArray, JSON_PRETTY_PRINT);
                echo $jsonEncodedReturnArray;
                
            }
            else {
                $returnArray = array('error' => 'Invalid user ID or password.');
                $jsonEncodedReturnArray = json_encode($returnArray, JSON_PRETTY_PRINT);
                echo $jsonEncodedReturnArray;
            }
            
            break;
        
        case 'GET':
            
            $token = null;
            
            if (isset($_GET['token'])) {$token = $_GET['token'];}
            
            if (!is_null($token)) {
                
                require_once('jwt.php');
                
                // Get our server-side secret key from a secure location.
                $serverKey = '5f2b5cdbe5194f10b3241568fe4e2b24';
                
                try {
                    $payload = JWT::decode($token, $serverKey, array('HS256'));
                    $returnArray = array('userId' => $payload->userId);
                    if (isset($payload->exp)) {
                        $returnArray['exp'] = date(DateTime::ISO8601, $payload->exp);;
                    }
                }
                catch(Exception $e) {
                    $returnArray = array('error' => $e->getMessage());
                }
            }
            else {
                $returnArray = array('error' => 'You are not logged in with a valid token.');
            }
            
            // return to caller
            $jsonEncodedReturnArray = json_encode($returnArray, JSON_PRETTY_PRINT);
            echo $jsonEncodedReturnArray;
            
            break;
        
        default:
            $returnArray = array('error' => 'You have requested an invalid method.');
            $jsonEncodedReturnArray = json_encode($returnArray, JSON_PRETTY_PRINT);
            echo $jsonEncodedReturnArray;
    }