@stavros, not sure if OSS is a requirement, but my current employer is in the same space.
It is not open source, but there is a gratis/free as in beer edition that you can download and use commercially (for certain usage: https://fusionauth.io/license-faq#3 ).
It's pretty great, but you should be aware that the LTS version is called red hat single sign on (rh sso), and the keycloak itself updates every few months.
It's usually not a deal breaker, but you should be aware if you're going to evaluate it for work
