How to generate JWT in PHP

Question

How to generate JWT token in php using with the following parameters Subject, Issuer, Expiry time and payload in the < PAYLOAD > tag.

• Id can be any random number of any length.
• subject is TestService
• Issuer is Baguma Inc
• Expiry Time will be 30 sec from current time(ideally ).
• Payload is the request from Third Party
• SigningKEY is fcvxcnfrhrtghkfghgwerikdf
• Signature algorithm will be HS512.

Sample request from Third Party is shown below

<COMMAND><TYPE>REQUEST</TYPE><INTERFACE>TESTACCOUNT</INTERFACE> <REQUESTID>123</REQUESTID></COMMAND

Answer 1

With the help of an article from DZone Security, I managed to generate a JWT token by doing the following

1. Define the base64UrlEncode function which replaces + with -, / with _ and = with ''.

function base64UrlEncode($text)
{
    return str_replace(
        ['+', '/', '='],
        ['-', '_', ''],
        base64_encode($text)
    );
}

2. Encode the headers using base64UrlEncode

$headers = [ "alg" => "HS512"];

$headers_encoded = $this->base64UrlEncode(json_encode($headers));

3. Encode the Payload using Base64 URL encode as well

$issuedAt = time();

    $payload =  [
        "id" =>$this->gen_uuid(), //   .setId(UUID.randomUUID().toString())
        "sub"=> "TestService", //Subject
        "exp"=> $issuedAt+30,
        "iss"=> "Baguma Inc",  //issuer
        "iat"=> $issuedAt,  //issued at
        "PAYLOAD"=> "<COMMAND><TYPE>REQUEST</TYPE><INTERFACE>TESTACCOUNT</INTERFACE> <REQUESTID>123</REQUESTID></COMMAND"];

      $payload_encoded = $this->base64UrlEncode(json_encode($payload));

4. Using the Key/secret build the signature

$key = "fcvxcnfrhrtghkfghgwerikdf";  
$signature = hash_hmac('sha512',"$headers_encoded.$payload_encoded",$key,true);

5 Encode the signature

$signature_encoded = $this->base64UrlEncode($signature);

6. Build and return the token

$token = "$headers_encoded.$payload_encoded.$signature_encoded";