I cant find any description on how to read custom http request headers in a REST service.

On some occations i want to read http headers passed along when customers uses our REST API or headers added by the CND provider. Does anyone know how to read these http headers?

For example:
cloudflair.com sends a vistors country information along to the server using a customer http header called "CF-IPCountry". We would like to read this information and use it for statistics.