(PHP 5 >= 5.2.0, PHP 7, PHP 8)
openssl_csr_get_subject — Returns the subject of a CSR
$csr, bool $short_names = true): array|false
   openssl_csr_get_subject() returns subject
   distinguished name information encoded in the csr
    including fields commonName (CN), organizationName (O), countryName (C) etc.
  
csrSee CSR parameters for a list of valid values.
short_names
       shortnames controls how the data is indexed in the
       array - if shortnames is true (the default) then
       fields will be indexed with the short name form, otherwise, the long name
       form will be used - e.g.: CN is the shortname form of commonName.
      
   Returns an associative array with subject description,  or false on failure.
  
| Version | Description | 
|---|---|
| 8.0.0 | csraccepts an OpenSSLCertificateSigningRequest instance now;
       previously, a resource of typeOpenSSL X.509 CSRwas accepted. | 
Example #1 openssl_csr_get_subject() example
<?php
$subject = array(
    "countryName" => "CA",
    "stateOrProvinceName" => "Alberta",
    "localityName" => "Calgary",
    "organizationName" => "XYZ Widgets Inc",
    "organizationalUnitName" => "PHP Documentation Team",
    "commonName" => "Wez Furlong",
    "emailAddress" => "wez@example.com",
);
$private_key = openssl_pkey_new(array(
    "private_key_bits" => 2048,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
));
$configargs = array(
    'digest_alg' => 'sha512WithRSAEncryption'
);
$csr = openssl_csr_new($subject, $privkey, $configargs);
print_r(openssl_csr_get_subject($csr));
?>
The above example will output something similar to:
Array
(
    [C] => CA
    [ST] => Alberta
    [L] => Calgary
    [O] => XYZ Widgets Inc
    [OU] => PHP Documentation Team
    [CN] => Wez Furlong
    [emailAddress] => wez@example.com
)