Mashery Support Portals Developer Blog
We launched a nice small feature today that allows you to configure Mashery to inject the ID of the API being consumed into the call headers that are passed to your API hosts. This ID is primarily used by the Mashery API. You use it to direct the Mashery API to perform operations on your configuration data that resides in Mashery. You might, for example, read in this ID and use it as an input parameter in an inline API call you make to Mashery to lookup an application name or an attribute of the partner's registration information.
You may toggle this feature on by navigating to the API Settings->Endpoints->Properties page. There you will find the option for "Pass X-Mashery-Service-Key Header in Request" with a yes/no option. When set to 'Yes', inbound calls to your API will receive a new header of X-Mashery-Service-Key with the API ID for it's value.