Okta SSO as en extra auth method

Can anyone please point me to a guide on how to add Okta SSO as an extra auth method, additionally to an existing auth method used in an application?

Use case: we want to use Okta SSO for most of the users, but leave secret fallback url for standard login with credentials for non-real users, that don’t have an Okta account

You can implement it on the application level. If user hits /login - use OktaSSO, if /oldLogin - use your local credential store to authenticate your users.