536310 Unique random access code upon completion of PayPal Payment

Hello, I almost have the complete process that I need for my website, however I need a solution to the final step of the process. Which is the delivery of a unique randomized access code. My current process is: 1) The user click a link to make a subscription payment via PayPal. 2) Once payment is complete the user is redirected to a [login to view URL] form to submit their personal details. 3)(This is the step I need your help) I need a method of randomly generating a unique access code that will work with my current admin setup (which is a manual enter access code and redirect URL) I'm thinking that I maybe able to omit step 2 from above as PayPal will fulfill that step when it collects payment. So for step 3 I could use a script that auto generates an access code and emails it to the user. Please let me know of any other solutions. Thank you highly! Jason J.