Do I understand correctly that Oauth is a standard, and everyone implements it differently?

Question

OAuth

Lamersky question, I do not argue. But still:
There is an OAuth 2.0 specification, do I understand correctly that if I want to add my OAuth to my service (not Facebook, Twitter, but for my site), then I myself decide how to generate, for example, an access_token (when I have one will be asked), how to issue a refresh_token, what scopes are available, etc.
Those. there is no any, or third-party service that will have to do this for me, right? You have to do it all yourself

Answer 1

You can do it yourself, yes. Or you can use a ready-made Identity Server (installed or SaaS).
Examples:
Premises:
- Keycloak
- WSO2
- IdentityServer4
- ...
SaaS:
- Auth0
- Okta
- Onelogin
- AWS Cognito
- ...