On the page Access Managers you can see that there exist several ones, just not for OAuth 2
.
For OAuth 2
an Access Manager had to be developed, perhaps it's possible on base of the existing ones.
Having a look at some commits concerning OpenID
there exist the following list:
It seems being mixed in core though, so probably it's impracticable to do it in the same kind as core can't be updated anymore without problems.
On the other hand, if you are willing to provide the new Access Manager directly to core-development it wouldn't matter, but then it's advisable to contact the core-developers on github first.
While REST might serve as interface for a separated module, the authentication process is technically explained as Provisioning Service
.
In Extensions you get an impression which extensions exist and you'd to verify them to get knowledge how to solve your approach in an own extension. I'd chose perhaps SAML 2.0 Service Provider as it's also related to authentication.
Concerning OAuth 2
itself there exist a few implementations in github, regrettable only in PHP, but perhaps that helps you a bit.