I'm building a new app that needs to authorize and reserves funds from a user to be collected much later (perhaps a month), similar to Kickstarter.<p>What is the best way to do this from a web app?
You might want to have a look at Amazon's Flexible Payment System (FPS):
<a href="https://payments.amazon.com/sdui/sdui/business?sn=devfps/o" rel="nofollow">https://payments.amazon.com/sdui/sdui/business?sn=devfps/o</a>