Use a private key from a file.
void use_private_key_file( const std::string & filename, file_format format, asio::error_code & ec);
This function is used to load a private key into the context from a file.
The name of the file containing the private key.
The file format (ASN.1 or PEM).
Set to indicate what error occurred, if any.
Calls SSL_CTX_use_PrivateKey_file
.