Azure API Management is a cloud hosted service that can add many capabilities to an existing HTTP API on any platform. This includes functions related to security, API key management, caching, documentation, and many other cross cutting policies.
For more info, see http://azure.microsoft.com/apim.
Here is some getting start info:
https://azure.microsoft.com/en-us/documentation/articles/api-management-key-concepts/
Here is the APIM policy reference:
https://azure.microsoft.com/en-us/documentation/articles/api-management-policy-reference/