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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

The same-origin policy

Sooner or later, web developers run up against the same-origin policy. Maybe you want to trigger a script on one domain and use the results on a different domain, but you can't.

The same-origin policy is necessary for web application security. The execution of a script may expose sensitive information. Access to this information is limited to the same domain where the script is located, unless access for an external domain has been specifically allowed by code.

Note

The same-origin policy is defined by the Internet Engineering Task Force (IETF) (https://tools.ietf.org/html/rfc6454#page-4).

A major motivation for implementing the same-origin policy is to protect sensitive information stored in cookies from being exposed to another domain. Web applications maintain authenticated user sessions in cookies. The user's personalizations and account information are stored in cookies. To ensure data confidentiality, cookies may not be shared across domains. For cookies, the same origin is shared by the domain or a sub-domain of that domain. For DOM elements such as scripts, the restrictions are more fine-grained.

The same-origin policy also applies to requests made with XMLHttpRequest (XHR). We will see how the Access-Control-Allow-Origin header facilitates the bending of the same-origin policy.

Notably, JSON-P, WebSocket, and window.postMessage are not restricted by the same-origin policy.

End of Section 2
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