I am trying to set up ngix as a reverse proxy server. My webserver/application requires the following flow for authentication and application login:

From remote client:
User requests URL from a browser --> (Works)
User is authenticated to webserver using certificate --> (Works)
Request is redirected to application SSO server from the webserver--> (See that above address bar in browser window)
Request is redirected back to Webserver from application server --> (Never seen when going thru ngix proxy)
User presented with application. (Never seen when going thru ngix proxy server)
User is presented with error that displays my INTERNAL servers name (which is correct for the handoff for the SSO). Its as if that server is trying to answer externally to the client request instead of sending the request back to the webserver and the webserver sending the request back to the client thru the ngix reverse proxy server.

No matter how I configure the ngix reverse proxy, It always fails with a DNS error of the application SSO servers name whic is not exposed externally. Same goes for the webserver.

However, it DOES work when I access the webserver from a browser window on the same server that is running ngix reverse proxy.
From server running ngix:
User requests URL from a browser --> (Works)
User is authenticated to webserver using certificate --> (Works)
Request is redirected to application SSO server from the webserver--> (Works)
Request is redirected back to Webserver from application server --> (Works)
User presented with application. (Works)

How can I configure NGIX to allow for the webserver handoff to the SSO server so that it doesnt try to return the SSO server to the users browser?