The .NET SDK (Software Development Kit) plays a crucial role in ASP.NET Core development by providing the tools necessary for building and compiling ASP.NET Core applications. It includes the command-line interface (CLI) tools like 'dotnet' for project management, building, and running applications. Debugging, database management, and web server request handling are tasks typically handled by other components of the development stack.

In an ASP.NET Core application, it's not secure to expose sensitive information like a production database connection string in appsettings.json. To securely manage it, you should store it in an environment variable. This approach helps protect sensitive data from accidental exposure and is a best practice for configuration management in production environments.

In an ASP.NET Core project, the .csproj (C# project) file is crucial for specifying the SDK version, dependencies, and various project-related configurations. It serves as the project file that orchestrates the build process and defines the project structure.

The DbContext class in Entity Framework Core serves as the bridge between your application code and the database. Its primary purpose is to manage database connections, handle database operations, and provide a high-level data access API for interacting with the database. It abstracts the underlying database operations, making it easier to work with databases in your application.

The "Web Application (Razor Pages)" template uses server-side rendering, where most of the processing occurs on the server before rendering content to the client. This can be a scalability bottleneck for large-scale applications with high traffic because it places a significant load on the server. Web APIs and client-side rendering approaches like Blazor Server are typically preferred for such scenarios.

The correct file to specify the default layout for Razor views in ASP.NET Core is _ViewStart.cshtml. This file allows you to set the layout that should be applied to multiple views in a folder or the entire application.

In an ASP.NET Core MVC application, information about available books and their details is typically stored in a database. The Model (M) in MVC is responsible for managing data, and databases are commonly used for persistent data storage in such applications. Controllers handle user requests and orchestrate interactions with the Model to retrieve and display this data.

To create a user programmatically in ASP.NET Core Identity, you would typically make use of the CreateAsync method provided by the UserManager class. This method allows you to create a new user by specifying their details and asynchronously adds them to the user store.

The primary purpose of the [Authorize] attribute is to restrict access to specific actions or controllers within an ASP.NET Core application. It helps in implementing authentication and authorization by allowing only authorized users to access certain parts of the application. This attribute is crucial for securing web applications and ensuring that sensitive functionality is protected.

The feature that would help you accomplish this is ASP.NET Core Identity. Identity is a membership system that enables you to add authentication and authorization features to your application, including user account management. It provides features like user registration and login.