Chapter 1, Why You Need CORS, discusses the same-origin policy, which limits sharing resources across domains; granting access to CORS requests by setting headers; different ways to add more security; understanding preflight requests to prepare for some types of CORS methods and events; and alternatives to CORS.

Chapter 2, Creating Proxies for CORS, discusses what a Proxy Server is and various reasons to use a Proxy, different types of Proxy Servers, and reverse proxis in Node.js with CORS anywhere.

Chapter 3, Usability and Security, discusses CORS and XDomainRequest, detecting AJAX support in the browser, using preflight to ensure usability and improve security, handling access-control-allow-origin header with and without the wildcard, HTTP request and response headers for usability and security, CORS requests with credentials, and setting and reading cookies, and CORS security cheat sheet by OWASP.

Chapter 4, CORS in Popular Content Management Frameworks, discusses how to enable CORS in WordPress, Drupal, Joomla!, and Adobe Experience Manager (AEM).

Chapter 5, CORS in Windows, discusses implementing CORS on the Windows platform. The Windows platform includes IIS, ASP.NET Web API applications, and Windows Communication Foundation.

Chapter 6, CORS in the Cloud, discusses using CORS in cloud computing services such as Amazon Simple Storage Service (S3), Google Cloud Storage, IBM Cloudant, Windows Azure Storage, the Box.com API, and the Dropbox API.

Chapter 7, CORS in Node.js, discusses the Node.js platform and using CORS in JavaScript frameworks such as ReactJS, Ember.js, and Socket.IO, with examples based on the fundamentals of CORS with allowed origin(s), methods, and headers.

Chapter 8, CORS Best Practices, discusses best practices in enabling API-to-public CORS requests, limiting the API to allow CORS requests to a whitelisted set of origins, protecting against cross-site request forgery (CSRF), and minimizing preflight requests.

This book is intended for any web developer who works on various web applications with different technologies, developers who create APIs for external applications to consume, and developers who ensure security when cross-origin resource sharing happens.

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, path names, dummy URLs, user input, and Twitter handles are shown as follows: "Media files with the <video> and <audio> tags as long as the file type matches expected media formats."

A block of code is set as follows:

public static class WebApiConfig
{
  public static void Register(HttpConfiguration config)
  {
    // Other configurations omitted config.EnableCors();
    config.SetCorsPolicyProviderFactory(
      new DynamicPolicyProviderFactory());
  }
}

Any command-line input or output is written as follows:

PM> Install-Package Microsoft.AspNet.WebApi.Cors

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Clicking the Next button moves you to the next screen".

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