Adobe I/O - Creating Access Token (3rd Party Vendor)

Hello, 

I have a situation where a 3rd Party Vendor is in charge of my clients Website. I set up an Order Confirmation and Password Reset Event for Transactional Messaging in ACS. The 3rd party vendor will be providing the data identified in the Event that populates the ctx. Here's what I've done so far

1) I create a project in Adobe I/O to generate a JWT Token. I understand this token is to be used in order to generate the Access Token

2) I was able to create and test the Events/Transactional Messaging and send myself the emails. 

However, here is where I run into problems. I understand the Access Tokens are only good for 24 hrs and must be refreshed - however, I can't find any documentation that would explain how to refresh the token daily, other than manually logging into the Adobe Console UI, and going through the steps to generate that JWT and Access Tokens. 

There's got to be a way for a 3rd Party to gain access via script, where they would use the Private Key (I've provided it to them) to generate the token, then use the Token to generate the Access Token. 

My other question is, am I even using the correct service for this process? Should I be using OAuth or API Key authentication?