I'm not sure I understand your question. I'd use OIDC for the login form, but the whole point of OAuth (at least the authorization code grant) is that the login process happens at a third party (FusionAuth in this instance).
If you want to have the user login and control the whole process (including your own pages), use the login API, or, if you must use an OAuth grant, the password grant.
Please feel free to give more information about your question, as again, I'm not sure I understood it.