cURL and You are not authorized to perform this action

Hi Support, I am trying to use cURL to forward a post to index.php for member registration. I get the error You are not authorized to perform this action. I have the same XID_hash in exp_security_hashes as the one I am passing in via CURLOPT_POSTFIELDS. The XID hidden field I am hard coding in the form looks like this.

<input type="hidden" name="XID" value="{XID_HASH}" />

When I turn off Secure Form Mode, the registration works. Obviously, I want to have secure form mode on. I am submitting the form to itself and processing the post via php and calling cURL. What else can I do to make this work with secure mode on? Thanks, Dave