Fastly - how to Purge by Surrogate Key

The Fastly CDN allows for fast, sub-second purging of content. 

The regular purge command is by URL, for example like this: 

curl -X PURGE http://url-of-asset-to-purge 

To have better context sensitive control over the purging process, you can associate a surrogate key to every piece of content and then purge by key. 

To associate a surrogate key with content, add a header on your origin that specifies at least one surrogate key. Related content can share the same key. 

HTTP/1.1 200 OK
Surrogate-Key: key1 key2 key3
Content-Type: text/html

To purge a specific surrogate key, POST a request like this: 

 POST /service/<service-id>/purge/<surrogate-key>
 Fastly-Key: d3cafb4dde4dbeef 
 Accept: application/json 

Replace <service-id> and <surrogate-key>  with your values

Links: 
http://www.fastly.com/blog/surrogate-keys-part-1#.UvpEiWKSw7s
https://fastly.zendesk.com/entries/21921227-How-can-I-purge-content-on-Fastly-
http://docs.fastly.com/api/purge#purge_3