[SRE-4642] Add original-x-forwarded header handling

[zacblazic]

Overview

Adds the ability to set X-Forwarded-* headers using a priority-based approach.

Going forward, the values of X-Original-Forwarded-* headers will be used if they exist, otherwise we fall back to the previous default values.

Examples

With X-Original-Forwarded-* headers

Incoming request:

X-Forwarded-Host: www.example.com
X-Forwarded-Port: 80
X-Forwarded-Proto: http
X-Forwarded-Ssl: off
...
X-Original-Forwarded-Host: app.example.com
X-Original-Forwarded-Port: 443
X-Original-Forwarded-Proto: https
X-Original-Forwarded-Ssl: on

Outgoing proxy request:

X-Forwarded-Host: app.sandbox.zappi.io
X-Forwarded-Port: 443
X-Forwarded-Proto: https
X-Forwarded-Ssl: on

Without X-Original-Forwarded-* headers

Incoming request:

X-Forwarded-Host: www.example.com
X-Forwarded-Port: 80
X-Forwarded-Proto: http
X-Forwarded-Ssl: off

Outgoing proxy request:

X-Forwarded-Host: www.example.com
X-Forwarded-Port: 80
X-Forwarded-Proto: http
X-Forwarded-Ssl: off

[itskingori]

👍🏽