I think it would be a good idea to take a step back and ask what is it that you’re trying to achieve.
Userbase, the service linked, is a backend as a service platform that offers you authentication and basic database that you can access via their api. You’d then code your own front end web app to interact with their service and store data there. You pay only per storage used by their storage tiers, which are frankly fairly fair priced. If that is something you’d need, that’s a good idea, but you’d be coding the front end yourself.
If you’re only looking for authentication with OAuth, and then coding your own API backend, then something like Authentik would be a nice self hosted authentication provider. Others that commonly gets mentioned but I’ve got limited/no experience with worlds new keycloak, or fusionauth. Managed services here would be your Auth0, Okta, etc.
If you’ve got a specific use case in mind, then it may be a good idea to say what service you’re thinking about, and the community may be able to suggest prebuilt solutions that good better and require less lift.
The industry by and large have moved on to containers, with docker being the entry point and eventually graduating to something larger and more orchestrated like k8s.
You’d generally use a publisher container (I.e. php:latest), and then volume mount your code into it for development, and eventually baking your own image for deployment. Be mindful to not include secrets (API keys, passwords, etc.) and inject them via environment variables.