(PHP 4 >= 4.2.0, PHP 5, PHP 7, PHP 8)
openssl_pkey_export_to_file — Gets an exportable representation of a key into a file
$key,$output_filename,$passphrase = null,$options = null
   openssl_pkey_export_to_file() saves an ascii-armoured
   (PEM encoded) rendition of key into the file named
   by output_filename.  
  
Note: You need to have a valid openssl.cnf installed for this function to operate correctly. See the notes under the installation section for more information.
key
output_filenamePath to the output file.
passphrase
       The key can be optionally protected by a
       passphrase.
      
options
       options can be used to fine-tune the export
       process by specifying and/or overriding options for the openssl
       configuration file. See openssl_csr_new() for more
       information about options.
      
   Returns true on success or false on failure.
  
| Version | Description | 
|---|---|
| 8.0.0 | keyaccepts an OpenSSLAsymmetricKey
       or OpenSSLCertificate instance now;
       previously, a resource of typeOpenSSL keyorOpenSSL X.509was accepted. |