openssl_csr_get_public_key

<?php
$subject = array(
    "commonName" => "example.com",
);
$private_key = openssl_pkey_new(array(
    "private_key_bits" => 2048,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
));
$csr = openssl_csr_new($subject, $private_key, array('digest_alg' => 'sha256') );
$public_key = openssl_csr_get_public_key($csr);
$info = openssl_pkey_get_details($public_key);
echo $info['key'];
?>