Adding CORS

CORS stands for Cross-Origin Resource Sharing and is a mechanism that uses HTTP headers to tell a browser to let a web application run at certain origins (domains) so that it has permission to access certain resources on a server at a different origin.

In this section, we will start by trying to access our REST API from a browser application and discover that it isn't accessible. We will then add and configure CORS in the REST API and verify that it is accessible from a browser application.

Let's carry out the following steps:

1. Run the backend project by pressing F5 in Visual Studio.
2. In a browser, browse to https://resttesttest.com/ address. This is a browser application that we can use to check whether our REST API is accessible from a browser.
3. Enter the path to the questions endpoint and press the Ajax request button. We see that the request is unsuccessful:

   Figure 11.12 – CORS error when accessing the REST API from the browser

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