AWS V4 Signature Request Trait - requires AWS-PHP-SDK. Below example used in a Laravel app. Returns a signed request.

AwsV4SignedRequestTrait.php

<?php

namespace App\Traits;

use Psr\Http\Message\RequestInterface;
use Aws\Signature\SignatureV4;
use Aws\Credentials\CredentialProvider;
use Aws\Credentials\CredentialsInterface;

/**
 * APIGateway calls can require a V4 signiture created using the request headers.
 * This trait takes the service name and original request and updates with necessary headers.
 *
 * e.g
 * $req = new GuzzleHttp\Psr7\Request("POST","https://awsgatewayapi.service-name.com/post",[],"{\"data\":\"some body data\"}");
 * $signedrequest = $this->getSignedRequest($req, "service-name");
 */
trait AwsV4SignedRequestTrait
{
    /**
     * @param RequestInterface $request unsigned request
     * @param string           $service Service name to use when signing
     *
     * @return RequestInterface signed request
     */
    public function getSignedRequest(RequestInterface $request, string $service): RequestInterface
    {
        $signitureV4 = new SignatureV4($service, config('app.awsRegion'));

        return $signitureV4->signRequest($request, $this->getAwsCredentials());
    }

    /**
     * @return CredentialsInterface AWS Credentials
     */
    private function getAwsCredentials(): CredentialsInterface
    {
        $provider = CredentialProvider::defaultProvider();
        return $provider()->wait();
    }
}