As I wrote in a sibling comment: Keycloak, for one: https://www.keycloak.org https://www.keycloak.org I've also heard good things about Hydra: https://www.ory

As I wrote in a sibling comment: Keycloak, for one: https://www.keycloak.org https://www.keycloak.org I've also heard good things about Hydra: https://www.ory.sh/hydra/ https://www.ory.sh/hydra/ Depending on your needs, an SSO proxy like Vouch works well for internal services: https://github.com/vouch/vouch-proxy https://github.com/vouch/vouch-proxy There's also an abundance of libraries for different programming languages to implement authentication or authorisation, lots of them battle-tested by thousands of services. It's not like providing secure services is impossible without Okta.