configargs is a list of arguments like those :
$configArgs = array(
"digest_alg" => "sha1",
"private_key_bits" => 1024,
"private_key_type" => OPENSSL_KEYTYPE_RSA,
);
digest_alg is the equivalent for default_md in openssl
private_key_bits is the length of the key
private_key_type is obvious... only RSA is supported for now i think.