( mixed key, string &out [, string passphrase [, array configargs]] )
openssl_pkey_export() exports key as a PEM encoded string and stores it into out (which is passed by reference).
The key is optionally protected by 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.
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.