API and authentication in curl call

I am looking to build a custom plugin on a Wordpress site.

Basically, when a user registers, the plugin will make a curl call to the SuiteCRM install and check if there is a Lead, Contact, or Target with either the same Wordpress Username (which would be a custom field made in SuiteCRM for those modules), or the same email address.

If the GET returns nothing, it would create a Target.

I am stuck at how authentication works, however.

The closest I have done is calling to Twilio in which I used curl_setopt($ch, CURLOPT_USERPWD,$TWILIO_SID . ':' . $TWILIO_TOKEN);

Using a specific user doesn’t necessarily make sense, though…

If I want to use Client ID/Secret, how do I pass that with my Curl call on the Wordpress side?