The Axway Vordel API Gateway allows you to read in REST API parameters from an incoming request, and then use these parameters for a variety of purposes, for example to pass them into a SOAP message, or use them to call a method of a Java class via the Scripting Filter.
The key to this is the "Extract REST Request Attributes" filter. If I type in "REST" into the search box on Policy Studio, it helpfully narrows down the filter list to just the filters related to REST.
When I drag in an "Extract REST Request Attributes" filter, I see this configuration below. As you can see, you can have the API Gateway read API parameters from the querystring or from HTTP POST parameters.
Once I place this filter into a policy which is mapped to a REST endpoint on the API Gateway (e.g. a relative path), I can then access the REST parameters in other filters.
Let's say a parameter is passed like this:
I can now access the content of the "customerID" parameter like this: