Added information about CORS support

README.md

@@ -102,6 +102,67 @@ window.authorizations.add("key", new ApiKeyAuthorization("Authorization", "XXXX"
 
 Note!  You can pass multiple header params on a single request, just use unique names for them (`key` is used in the above example).
 
+## CORS Support
+
+CORS is a technique to prevent websites from doing bad things with your personal data.  Most browsers + javascript toolkits not only support CORS but enforce it, which has implications for your API server which supports Swagger.
+
+You can read about CORS here: http://www.w3.org/TR/cors.
+
+There are two cases where no action is needed for CORS support:
+
+1. swagger-ui is hosted on the same server as the application itself (same host *and* port).
+2. The application is located behind a proxy that enables the requires CORS headers. This may already be covered within your organization.
+
+Otherwise, CORS support needs to be enabled for:
+
+1. Your Swagger docs. For Swagger 2.0 it's the `swagger.json` and any externally `$ref`ed docs, and for prior version it's the `Resource Listing` and `API Declaration` files.
+2. For the `Try it now` button to work, CORS needs to be enabled on your API endpoints as well.
+
+### Testing CORS Support
+
+You can verify CORS support with one of three techniques:
+
+- Curl your API and inspect the headers.  For instance:
+
+```bash
+$ curl -I "http://petstore.swagger.wordnik.com/api/api-docs"
+HTTP/1.1 200 OK
+Date: Thu, 12 Sep 2013 17:05:44 GMT
+Access-Control-Allow-Origin: *
+Access-Control-Allow-Methods: GET, POST, DELETE, PUT, PATCH, OPTIONS
+Access-Control-Allow-Headers: Content-Type, api_key, Authorization
+Content-Type: application/json
+Content-Length: 0
+```
+
+This tells us that the petstore resource listing supports OPTIONS, and the following headers:  `Content-Type`, `api_key`, `Authorization`.
+
+- Try swagger-ui from your file system and look at the debug console.  If CORS is not enabled, you'll see something like this:
+
+```
+XMLHttpRequest cannot load http://sad.server.com/v2/api-docs. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access. 
+```
+
+Swagger-UI cannot easily show this error state.
+
+- Using the http://www.test-cors.org website. Keep in mind this will show a successful result even if `Access-Control-Allow-Headers` is not available, which is still required for Swagger-UI to function properly.
+
+### Enabling CORS
+
+The method of enabling CORS depends on the server and/or framework you use to host your application. http://enable-cors.org provides information on how to enable CORS in some common web servers.
+
+Other servers/frameworks may provide you information on how to enable it specifically in their use case.
+
+### CORS and Header Parameters
+
+Swagger lets you easily send headers as parameters to requests.  The name of these headers *MUST* be supported in your CORS configuration as well.  From our example above:
+
+```
+Access-Control-Allow-Headers: Content-Type, api_key, Authorization
+```
+
+Only headers with these names will be allowed to be sent by Swagger-UI.
+
 ## How to Improve It
 
 Create your own fork of [swagger-api/swagger-ui](https://github.com/swagger-api/swagger-ui)