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CORS Essentials

CORS Essentials

By : Gunasundaram
3 (1)
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CORS Essentials

CORS Essentials

3 (1)
By: Gunasundaram

Overview of this book

This book explains how to use CORS, including specific implementations for platforms such as Drupal, WordPress, IIS Server, ASP.NET, JBoss, Windows Azure, and Salesforce, as well as how to use CORS in the Cloud on Amazon AWS, YouTube, Mulesoft, and others. It examines limitations, security risks, and alternatives to CORS. It explores the W3C Specification and major developer documentation sources about CORS. It attempts to predict what kinds of extension to the CORS specification, or completely new techniques, will come in the future to address the limitations of CORS Web developers will learn how to share code and assets across domains with CORS. They will learn a variety of techniques that are rather similar in their method and syntax. The book is organized by similar types of framework and application, so it can be used as a reference. Developers will learn about special cases, such as when a proxy is necessary. And they will learn about some alternative techniques that achieve similar goals, and when they may be preferable to using CORS
Table of Contents (10 chapters)
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Preface
Preface
What this book covers
What you need for this book
Who this book is for
Conventions
Reader feedback
Free Chapter
1
1. Why You Need CORS
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1. Why You Need CORS
The same-origin policy
Considering the origin of entities
Commonly allowed cross-origin resource sharing
Permissions required by JavaScript
How CORS works – the header and the request
CORS with Preflight
Troubleshooting and debugging CORS
CORS with jQuery
Enabling CORS globally with server configuration
Alternatives to CORS
Summary
2
2. Creating Proxies for CORS
2. Creating Proxies for CORS
Proxies and the World Wide Web
What is a proxy server?
Reasons to use a proxy
Creating a proxy server with Google App Engine
Summary
3
3. Usability and Security
3. Usability and Security
CORS usability
Enhancing security in CORS
Summary
4
4. CORS in Popular Content Management Frameworks
4. CORS in Popular Content Management Frameworks
Incoming CORS requests
SAAS or self-hosted?
CORS in WordPress
CORS in Drupal
CORS in Joomla!
CORS in Adobe Experience Manager
Summary
5
5. CORS in Windows
5. CORS in Windows
Incoming CORS requests
How to set the Access-Control-Allow-Origin header globally in Windows IIS Server
CORS in the ASP.NET Web API
CORS in Windows Communication Foundation
CORS in Windows browsers – Internet Explorer and Edge
Summary
6
6. CORS in the Cloud
6. CORS in the Cloud
CORS requests in cloud APIs
CORS in Amazon Simple Storage Service (S3)
Using CORS in Google Cloud Storage
Authenticated access to Google APIs with CORS
CORS in IBM Cloudant
CORS in Windows Azure Storage
CORS in Box API
CORS in the Dropbox API
Summary
References
7
7. CORS in Node.js
7. CORS in Node.js
JavaScript frameworks are very popular
Introduction to Node.js
JavaScript frameworks that work with Node.js
CORS in Express.js
CORS npm for Express.js using Connect.js middleware
CORS in AngularJS
CORS in Backbone.js
Node.js and JavaScript frameworks are evolving rapidly
Summary
References
8
8. CORS Best Practices
8. CORS Best Practices
Enabling API to public CORS requests
Limiting API to allow CORS requests to a whitelisted set of origins
Protecting against cross-site request forgery (CSRF)
Summary
9
Index
Index

Considering the origin of entities

Access to DOM elements is allowed only when the request scheme, hostname, and port number match those of the current URI. A subdomain cannot share DOM elements with the parent domain.

  • Scheme in web applications is typically http:// or https://
  • Hostname is typically the domain name plus TLD, or the unique IP address
  • Port number:
    • Typically, port 80 is implicit in http://
    • 443 for SSL over https://

If the Scheme, Hostname, and port number do not match the DOM element, then resource sharing is prohibited as they do not share the same origin. Considering the domain http://www.example.com, the following table provides various combinations of matching and mismatching origins:

URI

Match?

Reason

http://www.example.com/dir1/page1.html

Match

Same protocol and host

http://username:[email protected]/dir2/otherpage.html

Match

Same protocol and host

http://example.com/dir/page1.html

Mismatch

Different host (www is a subdomain)

https://www.example.com/dir/page1html

Mismatch

Different protocol(https://)

http://www.example.com:81/dir/page1.html

Mismatch

Same protocol and host but different port (81)

http://en.example.com/dir/page1.html

Mismatch

Different host (en is a subdomain)

Internet Explorer exception policy

Internet Explorer (IE) implements two major differences when it comes to the same-origin policy:

  • IE Trust Zones allow different domains: If both domains are in a highly trusted zone, then the same-origin policy limitations are not applied.
  • Port is ignored: IE ignores the port in same origin components. These URIs are considered from the same origin:
    • http://www.example.com:80/dir/page1.html
    • http://www.example.com:81/dir/page1.html

      Tip

      These exceptions in Internet Explorer are non-standard and are not supported in other browsers. If an application is only viewed in Windows RT mobile or Internet Explorer, then these exceptions could be useful.

End of Section 3
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