Which of the following enables user authentication in Mendix?

User authentication in Mendix is primarily enabled through the security settings in the Modeler. These settings allow developers to configure access roles, define user privileges, manage user registrations, and establish password policies, thus creating a structured and secure environment for user authentication.

The Modeler provides an interface for specifying who can access what within the application. By setting up appropriate roles and permissions, developers can control access to different parts of the application based on user identity or group membership. This is essential for enforcing security and ensuring that only authorized users can access sensitive data or functionalities.

In contrast, custom scripts are not the primary means of authentication in Mendix; they may be used to extend functionality but are not the foundational aspect of user authentication. User input on every page does not inherently manage authentication, as it would require additional mechanisms to validate that input against stored credentials. Lastly, while public access may be a feature in some applications, it does not provide secure authentication and may expose the application to unauthorized access. Thus, relying on security settings in the Modeler is the proper method for implementing user authentication in Mendix applications.