Getting OperationName in RequestInterceptor

Question

I have implemented a custom requestor interceptor for the purpose of authenticating requests, similar to below. I am trying to get the operation name in ProcessRequest and unable to.

Can anyone let me know how do I get the operation name here?

public class SampleInterceptor: Microsoft.ServiceModel.Web.RequestInterceptor 
{ 
    public SampleInterceptor() : base(true) 
    { 
    }

    public override void ProcessRequest(ref System.ServiceModel.Channels.RequestContext requestContext) 
    { 
         //need the operation name here to authenticate

    }
}