openssl_pkey_export() exports key as a PEM encoded string and stores it into out (which is passed by reference).
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.
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.