( mixed key, string outfilename [, string passphrase [, array configargs]] )
openssl_pkey_export_to_file() saves an ascii-armoured
(PEM encoded) rendition of key into the file named
by outfilename. The key can be optionally
protected by a passphrase.
configargs 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 configargs.
Returns TRUE on success or FALSE on failure.
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.