(PHP 4 >= 4.2.0, PHP 5, PHP 7)
openssl_csr_export_to_file — Exports a CSR to a file
   openssl_csr_export_to_file() takes the Certificate
   Signing Request represented by csr and saves it
   in PEM format into the file named by outfilename.
  
csrSee CSR parameters for a list of valid values.
outfilenamePath to the output file.
notext
 The optional parameter notext affects
 the verbosity of the output; if it is FALSE, then additional human-readable
 information is included in the output. The default value of
 notext is TRUE.
   Returns TRUE on success or FALSE on failure.
  
Example #1 openssl_csr_export_to_file() example
<?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, $private_key, array('digest_alg' => 'sha384') );
openssl_pkey_export_to_file($private_key, 'example-priv.key');
// Along with the subject, the CSR contains the public key corresponding to the private key
openssl_csr_export_to_file($csr, 'example-csr.pem');
?>