I'm sure what I'm wanting to do is possible with nginx, but it's isn't clear to me how to achieve it. I'd like for nginx to be able to receive a browser request that is handed to a C module I will code that will alter the URI (based on values returned by a MySQL database). Then I would like the standard proxying abilities of nginx be used to proxy the content from a private BE to the client based on the altered URI.

My thinking is I need to use a C module for the URI rewrite since I need to alter it based on data from a database. It isn't obvious to me how to code this. I've been using ngx_http_rewrite_module.c as a guild, but there's a lot going on in the code. Is a simpler example available I might reference?

Also, the only URIs I'd like nginx to proxy are ones returned by the C module. I'd never want a URI submitted by a client to be proxied directly.

Any suggestions are appreciated!

I found what I was looking for here: http://www.evanmiller.org/nginx-modules-guide-advanced.html

The non obvious part for me is the various ways in which a handler can indicate it has completed doing what it needed to do and how it must return so as to allow other modules to pick up handling the request in the right stage of processing. In this case, returning ngx_http_internal_redirect() was what I needed to do.