There are two things that everybody misses about OAuth and they fly under the radar.
Nice to hear someone touch on one of them: you absolutely NEED to use a transaction as a distributed locking mechanism when you use a token.
This goes double/quadruple for refresh tokens. Use the same token more than once, and that user is now signed out.
It doesn't matter if your system runs on one machine or N machines; if you have more than one request with a refresh token attached in flight at once - happens all the time - you are signing out users, often via 500.
Refresh tokens are one-time use.
The other thing devs and auth frameworks miss is the "state" parameter.
Nice to hear someone touch on one of them: you absolutely NEED to use a transaction as a distributed locking mechanism when you use a token.
This goes double/quadruple for refresh tokens. Use the same token more than once, and that user is now signed out.
It doesn't matter if your system runs on one machine or N machines; if you have more than one request with a refresh token attached in flight at once - happens all the time - you are signing out users, often via 500.
Refresh tokens are one-time use.
The other thing devs and auth frameworks miss is the "state" parameter.