You can create a .NET Core MVC web application with Auth0 authentication and Twilio SendGrid email notifications for user registration, allowing you to securely implement authentication in your applications while also sending emails to users upon registration. To achieve this, you need to install the Auth0 .NET SDK, configure an Auth0 application, set up SendGrid, and add authentication to your MVC application. The process involves creating a new project, installing the necessary packages, configuring the Auth0 application, setting up SendGrid, and adding authentication to your application. Once complete, your application will have authentication configured, allowing you to secure pages with the `[Authorize]` annotation and navigate registered users on the Auth0 dashboard.