Laravel middleware for validating slack signing secret

SlackRequest.php

<?php

namespace App\Http\Middleware;

use Exception;
use Carbon\Carbon;
use Closure;
use Illuminate\Support\Facades\Log;

class SlackRequest
{
    /**
     * Validate a slack request
     * by the slack signing secret (not the token)
     *
     * @param  \Illuminate\Http\Request $request
     * @param  \Closure $next
     *
     * @return mixed
     * @throws Exception
     */
    public function handle($request, Closure $next)
    {
        // define the version number
        $version = 'v0';
        
        // load the secret, you also can load it from env(YOUR_OWN_SLACK_SECRET)
        $secret = config('services.slack.signing_secret');
        
        // get the payload
        $body = $request->getContent();

        // get the timestamp
        // and compare with the local time, according to the slack official documents
        // the gap should under 5 minutes
        $timestamp = $request->header('X-Slack-Request-Timestamp');
        if (Carbon::now()->diffInMinutes(Carbon::createFromTimestamp($timestamp)) > 5) {
            throw new Exception("Invalid timstamp, too much gap");
        }

        // generate the string base
        $sig_basestring = "{$version}:{$timestamp}:{$body}";

        // generate the local sign
        $hash = hash_hmac('sha256', $sig_basestring, $secret);
        $local_signature = "{$version}={$hash}";

        // get the remote sign
        $remote_signature = $request->header('X-Slack-Signature');

        // check two signs, if not match, throw an error
        if ($remote_signature !== $local_signature) {
            throw new Exception("Invalid signature");
        }

        return $next($request);
    }
}