When you use the password grant_type flow to access the authorization endpoint, you can pass a username and password value to the endpoint, this should authenticate the user so you do not hit a login page, however you still are made to authenticate through the login page.
1. create simple oauth2 provider and client with scopes and claims of cn & mail and simple display name and redirect_uri.
2. open incognito window.
3. access authorize endpoint with password grant flow, and user credentials.
4. observe as you are taken to datastore login.