proxy pass based on html header attribute

Although this isn't directly rails related, I am hopefull that I can get
some advice here.. :slight_smile:

I can't seem to find a way to configure nginx with the standard modules
included to proxy_pass based off a custom html header attribute. The
only possibility I came up with was to write a custom module in c and
then link it into nginx.

Does anyone know of an alternative to nginx that can accomplish this or
how to achieve this within nginx.