What HTTP headers does nginx send to SCGI and FastCGI application servers?

[Some Developer]

I've looked through the nginx source code and couldn't find a specific 
list of HTTP headers that nginx passes through to SCGI and FastCGI 
application servers.

I'm writing a simple SCGI and FastCGI application server in C++ and need 
to know what set of options are available to use.

Unfortunately I'm not in a position to run a debugger just yet as the 
library code is in the process of being created and I haven't got a 
daemon written yet to listen for connections.

Is there a list somewhere? I've looked through the CGI 1.1 specification 
and it mentions several headers that are sent but I'm pretty sure that 
nginx sends other headers as well.