TL;DR:

Is it (or would it be) possible to get the same access_token from one fetch_token request to another, provided that the user is the same?

Scenario:

1. An anonymous user authenticates with Stack Exchange on my website
2. He does some stuff which I save in my db (for instance he says he likes blue)
3. The day after, he visits my website again with another browser/computer
4. He tries to authenticate with his Stack Exchange account again
5. Obviously, I want to make sure that he logs on my site with the account he created in 1.

The problem:

Currently, the access_token given in 4. will be different than the one given in 1. which has the following downsides:

• Each time someone logs in my website with his Stack Exchange account, I can't simply use the access_token to check if the user already exists in my db. I have to make one more request to get his account_id and check with that
• Which in turn, also forces me to store Stack Exchange's account_id in my db