PHP implementation of JWT

JWT.php

<?php

/* 

// EXAMPLE USE

// construct web token manager
$jwt = new JWT("SecretKey");

// ^ init JWT with a server side secret key ^

// sign token
$token = $jwt->sign([
    "username" => "john doe"
    "role" => "admin"
]);

// ^ sign a token object and get a token string ^

// verify token
$jwt->verify($token);

// ^ if the verification is successful, the token object will be returned ^
// ^ if it isn't, it will return false ^

*/

class JWT {

    // declare private secret property
    private $secret;

    // init
    public function __construct($secret) {

        // store secret
        $this->secret = $secret;

    }

    // internal hash function
    private function hash($str) {
        
        return hash("sha256", $str);
    
    }

    // internal data encoding function
    // this function base64 encodes a JSON string representation of the given data
    // data being any object or array
    private function encode($data) {

        // encode as JSON, then base64 and then return the result
        return base64_encode(json_encode($data));
    
    }

    // internal string decoding function
    // this function decodes a base64 into a JSON string and then parses the JSON 
    // 
    private function decode($string) {

        return json_decode(base64_decode($string));
    
    }
 
    public function sign($payload = []) {

        // generate and encode header
        $header = $this->encode([
            "alg" => "SHA256",
            "typ" => "JWT"
        ]);
        
        // generate and append initiated at property
        $payload["iat"] = date("c");
        
        // encode payload
        $payload = $this->encode($payload);
        
        // fetch token secret
        $secret = $this->secret;

        // generate signature
        $signature = $this->hash($header . "." . $payload . $secret);

        return $header . "." . $payload . "." . $signature;

    }

    public function verify($token) {

        $parts = explode(".", $token);

        if (count($parts) <= 2) {
        
            // failed validation
            return false;
        
        }

        $header = $parts[0];

        $payload = $parts[1];

        $signature = $parts[2];

        $generatedSignature = $this->hash($header . "." . $payload . $this->secret);

        if ($signature == $generatedSignature) {

            try {

                $header = $this->decode($header);
    
                $payload = $this->decode($payload);
    
            } catch (exception $err) {
    
                return false;
    
            }

            return $payload;

        } else {
            
            return false;
        
        }

    }

}

?>