openssl_pkey_export_to_file() saves an ascii-armoured (PEM encoded) rendition of key into the file named by outfilename.
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.
Path to the output file.
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.