Use SHA-256 for CloudFront signed URLs

Thank you so much for your answer, I had a feeling there was no way to use SHA256 with CloudFront but wanted to make sure I wasn't missing anything (it seems like some other signed requests on AWS do use SHA256). If anyone knows of an alternative way to make make RSA-SHA1 signatures in PHP (that doesn't use openssl_sign) please let me know. Thank you again.

I don't know much about PHP, but I did some research and found that phpseclib might be useful. https://api.phpseclib.com/3.0/phpseclib3/Crypt/RSA/PrivateKey.html

Awesome find! Thank you so much. I can confirm that phpseclib3 can generate the required signatures. Here is my fallback code that can replace rsa_sha1_sign from the post I referenced in the question:

use phpseclib3\Crypt\PublicKeyLoader;
use phpseclib3\Crypt\RSA;

function rsa_sha1_sign_fallback($policy, $private_key_filename) {
    $key = PublicKeyLoader::load(file_get_contents($private_key_filename));
    $key = $key->withHash('sha1')->withPadding(RSA::SIGNATURE_PKCS1);
    $signature = $key->sign($policy);
    
    return $signature;
}