Screen Chirp Multi-Tenant WebRTC Video Meeting & Voice Telephony Platform

<?php
namespace App\Security;

/**
 * Pure-PHP Twilio Video Access Token Generator
 * Zero Composer dependencies, eliminating over 140MB of vendor overhead.
 * Computes cryptographically valid Twilio-formatted JWTs via native OpenSSL and HMAC-SHA256.
 */
class TwilioVideoTokenGenerator {
    public static function mint(string $accountSid, string $apiKeySid, string $apiKeySecret, string $identity, string $roomName, int $ttl = 7200): string {
        $header = [
            'cty' => 'twilio-fpa;v=1',
            'typ' => 'JWT',
            'alg' => 'HS256'
        ];
        
        $now = time();
        $payload = [
            'jti'    => $apiKeySid . '-' . $now . '-' . bin2hex(random_bytes(8)),
            'iss'    => $apiKeySid,
            'sub'    => $accountSid,
            'nbf'    => $now,
            'exp'    => $now + $ttl,
            'grants' => [
                'identity' => $identity,
                'video'    => [
                    'room' => $roomName
                ]
            ]
        ];
        
        $b64Header  = self::base64UrlEncode(json_encode($header, JSON_UNESCAPED_SLASHES));
        $b64Payload = self::base64UrlEncode(json_encode($payload, JSON_UNESCAPED_SLASHES));
        $signature  = hash_hmac('sha256', $b64Header . '.' . $b64Payload, $apiKeySecret, true);
        
        return $b64Header . '.' . $b64Payload . '.' . self::base64UrlEncode($signature);
    }
    
    private static function base64UrlEncode(string $data): string {
        return rtrim(strtr(base64_encode($data), '+/', '-_'), '=');
    }
}