How to pre-sign AWS API gateway requests invoking lambdas

presign_api_gateway_requests.php

<?php
use Aws\Credentials\Credentials;
use GuzzleHttp\Psr7\Request;
use Aws\Signature\SignatureV4;
use Aws\Sts\StsClient;
use GuzzleHttp\Client;

/**
 * Sandbox is IAM profile with the user permissions to:
 * 1- execute-api:Invoke against the API Gateway resource
 * 2- lambda:InvokeFunction against the Lambda function sitting behind API Gateway
 */
$region = "eu-west-1";
$profile = "sandbox";
$version = "latest";
$service = "execute-api";

$request = new Request(
    'GET',
    'https://zttxjunrjk.execute-api.eu-west-1.amazonaws.com/Prod/',
    []
);

$client = new StsClient([
    'profile' => $profile,
    'region' => $region,
    'version' => $version,
]);

// Generate session token
$result = $client->getSessionToken();

// Temp Credentials
$credentials = new Credentials(
    $result['Credentials']['AccessKeyId'],
    $result['Credentials']['SecretAccessKey'],
    $result['Credentials']['SessionToken']
);

// Construct a request signer
$signer = new SignatureV4($service, $region);

// Sign the request
$request = $signer->signRequest($request, $credentials);

// Send the request
try {
    $response = (new Client)->send($request);
} catch (Exception $exception) {
    $response = $exception->getResponse()->getBody(true);
    echo $response;
}

echo $response->getBody()->getContents();
?>