What is the best approach for storing OAuth2 tokens?

I’ve now got the main authentication working using OAuth2 with Xero. My aim isn’t to use it to log them in, it’s to retrieve and post invoice details so there’s a sync between my app and the Xero account.

I am browsing to the SC script in order to log into Xero and get the tokens but what’s the best way to store these so I can easily connect to Xero in App Connect to get/post data after that? I need a pointer as to how to approach this so I get it right from the outset.

Many thanks.