Create a redirect programmatically in a website-configured S3 bucket.

.env.template

AWS_ACCESS_KEY_ID=
AWS_SECRET_ACCESS_KEY=
AWS_REGION=
AWS_S3_BUCKET=
AWS_BUCKET_WEBSITE_URL=

composer.json

{
    "require": {
        "aws/aws-sdk-php": "^3.90",
        "vlucas/phpdotenv": "^3.3"
    }
}

index.php

<?php
require './vendor/autoload.php';

$dotenv = Dotenv\Dotenv::create(__DIR__);
$dotenv->load();

use Aws\Credentials\Credentials;
use GuzzleHttp\Promise;
use Aws\S3\S3Client;

// Custom credentials provider is used to grab credentials from .env.
// This circumvents AWS's magic lookup of env vars and makes us
// more flexible in naming variables et cetera.
function getAwsCredentialsProvider(): callable {
    return function () {
        return Promise\promise_for(
            new Credentials(getenv('AWS_ACCESS_KEY_ID'), getenv('AWS_SECRET_ACCESS_KEY'))
        );
    };
}

$s3Api = new S3Client([
    'region'      => getenv('AWS_REGION'),
    'version'     => 'latest',
    'credentials' => getAwsCredentialsProvider(),
    'http' => [
        'timeout' => 400
    ]
]);

$from = $_SERVER['argv'][1] ?? null;
$to = $_SERVER['argv'][2] ?? null;

if (!$from || !$to) {
    echo 'Insufficient arguments. Usage: php ' . basename(__FILE__) . ' /from /to';
    exit(1);
}

// Ensure full URL.
$url = preg_match('/^http/', $to)
    ? $to
    : rtrim(getenv('AWS_BUCKET_WEBSITE_URL'), '/') . '/' . ltrim($to, '/');

var_dump($s3Api->putObject(
    [
        'Bucket' => getenv('AWS_S3_BUCKET'),
        'Key' => ltrim($from, '/'),
        'ACL' => 'public-read',
        'WebsiteRedirectLocation' => $url
    ]
));