Better scheme detection based on RFC7239

[ioquatix]

It seems like X-Forwarded-* is officially deprecated in favour of Forwarded: *= as defined in https://tools.ietf.org/html/rfc7239

I believe would be a good idea for Rack to support this.

There is at least one area where modifications are required: Request#scheme.

There may be others.

I am happy to submit a PR, but I thought we should discuss this first.

[jeremy]

Positive on supporting Forwarded in preference to X-Forwarded-*, but without deprecation in Rack itself. RFC7239 has some notes on forward transition.

[ioquatix]

Yeah, in falcon I'm just setting both headers in my request proxy, and for the purpose of handling rack middleware I prefer X-Forwarded-For. I need to make a general purpose HTTP header parser which doesn't suck, so that I can extract the details from the Forwarded header in a more agnostic way.

[ioquatix]

Related PR: #1224

[jeremyevans]

This isn't a bug in rack, but a feature request, so I'm going to close this now. Let's continue the discussion in #1423.