PayPal checkout with order authorization?

[d3CLT]

I am an independent consultant using WHMCS for invoicing, billing, and support. I'd like to begin offering my services over the Internet, charging my customers for one hour of my time in advance and adjusting their order total following our session. Is there a way for WHMCS to accommodate PayPal's order authorization feature? If not, where should I begin looking to implement this myself in WHMCS?

 

I am still trying to wrap my head around the whole process, but this will serve as a good starting point. Thanks!