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JSON Web Tokens without Firebase JWT
I have created a few tutorials on how to use Firebase JWT to create and use JSON Web Tokens, but I decided to try to do it without a framework, using just PHP. In this article, you can see how I created my own simple JWT generator.
class JWT {
private $headers;
private $secret;
public function __construct()
{
$this->headers = [
'alg' => 'HS256', // we are using a SHA256 algorithm
'typ' => 'JWT', // JWT type
'iss' => 'jwt.local', // token issuer
'aud' => 'example.com' // token audience
];
$this->secret = 'thisIsASecret';
}
}Within this class, we will create our generate function. this function will generate our token to be used against our validator.
public function generate(array $payload): string
{
$headers = $this->encode(json_encode($this->headers)); // encode headers
$payload["exp"] = time() + 60; // add expiration to payload
$payload = $this->encode(json_encode($payload)); // encode payload
$signature = hash_hmac('SHA256', "$headers.$payload", $this->secret, true); // create SHA256 signature
$signature = $this->encode($signature); // encode signature
return "$headers.$payload.$signature";
}Within our generate function, we reference a encode function. This function will simply base64 encode our strings to be used by the token.
private function encode(string $str): string
{
return rtrim(strtr(base64_encode($str), '+/', '-_'), '='); // base64 encode string
}In this function, we take the generated token, and validate the strings, the encoding, and finally the time. I have it set for 1 minute so the token will expire after 1 minute to ensure it is used for a purpose.
public function is_valid(string $jwt): bool
{
$token = explode('.', $jwt); // explode token based on JWT breaks
if (!isset($token[1]) && !isset($token[2])) {
return false; // fails if the header and payload is not set
}
$headers = base64_decode($token[0]); // decode header, create variable
$payload = base64_decode($token[1]); // decode payload, create variable
$clientSignature = $token[2]; // create variable for signature
if (!json_decode($payload)) {
return false; // fails if payload does not decode
}
if ((json_decode($payload)->exp - time()) < 0) {
return false; // fails if expiration is greater than 0, setup for 1 minute
}
if (isset(json_decode($payload)->iss)) {
if (json_decode($headers)->iss != json_decode($payload)->iss) {
return false; // fails if issuers are not the same
}
} else {
return false; // fails if issuer is not set
}
if (isset(json_decode($payload)->aud)) {
if (json_decode($headers)->aud != json_decode($payload)->aud) {
return false; // fails if audiences are not the same
}
} else {
return false; // fails if audience is not set
}
$base64_header = $this->encode($headers);
$base64_payload = $this->encode($payload);
$signature = hash_hmac('SHA256', $base64_header . "." . $base64_payload, $this->secret, true);
$base64_signature = $this->encode($signature);
return ($base64_signature === $clientSignature);
}class JWT
{
private $headers;
private $secret;
public function __construct()
{
$this->headers = [
'alg' => 'HS256', // we are using a SHA256 algorithm
'typ' => 'JWT', // JWT type
'iss' => 'jwt.local', // token issuer
'aud' => 'example.com' // token audience
];
$this->secret = 'thisIsASecret'; // change this to your secret code
}
public function generate(array $payload): string
{
$headers = $this->encode(json_encode($this->headers)); // encode headers
$payload["exp"] = time() + 60; // add expiration to payload
$payload = $this->encode(json_encode($payload)); // encode payload
$signature = hash_hmac('SHA256', "$headers.$payload", $this->secret, true); // create SHA256 signature
$signature = $this->encode($signature); // encode signature
return "$headers.$payload.$signature";
}
private function encode(string $str): string
{
return rtrim(strtr(base64_encode($str), '+/', '-_'), '='); // base64 encode string
}
public function is_valid(string $jwt): bool
{
$token = explode('.', $jwt); // explode token based on JWT breaks
if (!isset($token[1]) && !isset($token[2])) {
return false; // fails if the header and payload is not set
}
$headers = base64_decode($token[0]); // decode header, create variable
$payload = base64_decode($token[1]); // decode payload, create variable
$clientSignature = $token[2]; // create variable for signature
if (!json_decode($payload)) {
return false; // fails if payload does not decode
}
if ((json_decode($payload)->exp - time()) < 0) {
return false; // fails if expiration is greater than 0, setup for 1 minute
}
if (isset(json_decode($payload)->iss)) {
if (json_decode($headers)->iss != json_decode($payload)->iss) {
return false; // fails if issuers are not the same
}
} else {
return false; // fails if issuer is not set
}
if (isset(json_decode($payload)->aud)) {
if (json_decode($headers)->aud != json_decode($payload)->aud) {
return false; // fails if audiences are not the same
}
} else {
return false; // fails if audience is not set
}
$base64_header = $this->encode($headers);
$base64_payload = $this->encode($payload);
$signature = hash_hmac('SHA256', $base64_header . "." . $base64_payload, $this->secret, true);
$base64_signature = $this->encode($signature);
return ($base64_signature === $clientSignature);
}
}It is a simple project, but works as intended. I have used Firebase JWT in the past but sometimes you just need a simple solution without having to import and entire library. I hope this helps for your next small project. You can download the class on my GitHub or subscribe on YouTube for more tutorials.
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