I wonder why this got downvoted. I looked over the alternatives a while back, and I thought Ory looked the best too, with Keycloak as a good number 2.

I agree with the OP that it's good to not be dependent on SaaS for something as central as user management.

I do agree with the others that it's best to write as little as possible of security critical code yourself. However, integrating with a third party OAuth thing can be hard (and leave plenty of room for security fuckups) especially if you have anything implemented at all already user-wise.