.NET Core is a general purpose development platform maintained by Microsoft and the .NET community on GitHub. It is cross-platform, supporting Windows, macOS and Linux, and can be used in device, cloud, and embedded/IoT scenarios.

The following characteristics best define .NET Core:

• Flexible deployment: Can be included in your app or installed side-by-side user- or machine-wide.
• Cross-platform: Runs on Windows, macOS and Linux; can be ported to other OSes. The supported Operating Systems (OS), CPUs and application scenarios will grow over time, provided by Microsoft, other companies, and individuals.
• Command-line tools: All product scenarios can be exercised at the command-line.
• Compatible: .NET Core is compatible with .NET Framework, Xamarin and Mono, via the - .NET Standard Library.
• Open source: The .NET Core platform is open source, using MIT and Apache 2 licenses. Documentation is licensed under CC-BY. .NET Core is a .NET Foundation project.
• Supported by Microsoft: .NET Core is supported by Microsoft, per .NET Core Support

Middleware is a software component that will determine how to process the request and decide whether to pass it to the next component in the application pipeline. Each middleware has a vary specific role and actions to preform on the request.

To use generic variants of IServiceProvider methods you have to include the following namespace:

using Microsoft.Extensions.DependencyInjection;

Browser security prevents a web page from making AJAX requests to another domain. This restriction is called the same-origin policy, and prevents a malicious site from reading sensitive data from another site. However, sometimes you might want to let other sites make cross-origin requests to your web app.

Cross Origin Resource Sharing (CORS) is a W3C standard that allows a server to relax the same-origin policy. Using CORS, a server can explicitly allow some cross-origin requests while rejecting others. CORS is safer and more flexible than earlier techniques such as JSONP.