Cloudflare Streams - Signed URL php example

Stream.php

<?php

class Stream
{
    /**
     * Signs a url token for the stream reproduction
     *
     * @param string $uid The stream uid.
     * @param array $key The key id and pem used for the signing.
     * @param string $exp Expiration; a unix epoch timestamp after which the token will not be accepted.
     * @param string $nbf notBefore; a unix epoch timestamp before which the token will not be accepted.
     *
     * https://dev.to/robdwaller/how-to-create-a-json-web-token-using-php-3gml
     * https://developers.cloudflare.com/stream/viewing-videos/securing-your-stream#creating-a-signing-key
     *
     */
    public static function signToken(string $uid, array $key, string $exp = null, string $nbf = null)
    {
        $privateKey = base64_decode($key['pem']);

        $header = ['alg' => 'RS256', 'kid' => $key['id']];
        $payload = ['sub' => $uid, 'kid' => $key['id']];

        if ($exp) {
            $payload['exp'] = $exp;
        }

        if ($nbf) {
            $payload['nbf'] = $nbf;
        }

        $encodedHeader = self::base64Url(json_encode($header));
        $encodedPayload = self::base64Url(json_encode($payload));

        openssl_sign("$encodedHeader.$encodedPayload", $signature, $privateKey, 'RSA-SHA256');

        $encodedSignature = self::base64Url($signature);

        return "$encodedHeader.$encodedPayload.$encodedSignature";
    }

    protected static function base64Url(string $data)
    {
        return str_replace(['+', '/', '='], ['-', '_', ''], base64_encode($data));
    }
}

Excellent dude, this helped me a lot too!!!