What type of SWA template application should an Okta Administrator use to create a custom application with Username, password, and submit button fields?

The best choice for creating a custom application that requires fields for a username, password, and a submit button is the Template Plugin App.

This type of template allows for more flexibility and customization when designing the application's login interface and authentication flow. It supports the integration of various authentication methods and can effectively handle custom logic and workflows. This makes it suitable for applications where a simple username and password combination need to be utilized along with additional custom coding or features.

The other options would not provide the same level of customization required for such applications. The Template Basic Auth App is generally used for simple authentication needs without extensive customizability. Template Traditional App often involves standard authentication flows without the capabilities for custom logic integration, and Template OAuth App is specifically designed for OAuth-based authentication, which does not align with the requirement for username and password fields directly in the app's interface. Therefore, Template Plugin App is the most appropriate choice for scenarios that involve a custom login experience.