Q:

Can I pass custom data in the HTTP header?

I have a whole bunch of web services each with several web methods. The consumers of these services are varied and many. I want to augment each of these web methods with an extra optional parameter (Int64 or Int32) but adding new methods with this extra (optional parameter) is a lot of work and getting the clients to use the new methods will be even more time consuming.
So I was wondering if I could allow the clients that wanted to take advantage of the new feature that this param provides could pass this Int in the HTTP header or some other way.
So the first question is can I pass an int in the HTTP header? If so, how would one do that in C#/ASP.NET?
Otherwise, what other suggestions do you have for tackling this problem?

A:

Its a bit unorthodox and I'm sure some purists would be upset at the idea (the headers should only be used for the transport of the message, and should not contain the semantics of the message).
Practically its doable, but you want to be sure all your clients can add these headers.  If your clients are using tools to call the web methods rather than generating the HTTP requests themselves (which I'd hope is the case) then there's a real chance this is a problem.
Why is it so hard to add these additional overloads of the methods?

A:

Yes it is allowed - but note that it may cut off the ability to use proxies and sometimes http aware firewalls (they tend to inspect and rewrite headers). 

A:

Request.Headers.Add("headername", "headervalue");
Response.Headers.Add("headername", "headervalue");

