Add support for oslo_middleware http_proxy_to_wsgi

This sets up the HTTPProxyToWSGI middleware in front of Octavia API. The
purpose of this middleware is to set up the request URL correctly in
the case there is a proxy (For instance, a loadbalancer such as HAProxy)
in front of Octavia API.

So, when TLS connections are terminated at the proxy, and one tries to
get the versions from the '/' resource from Octavia API, one will notice
that the protocol is incorrect; It will show 'http' instead of 'https'.
So this middleware handles such cases.

The HTTPProxyToWSGI is off by default and needs to be enabled via a
configuration value.

It can be enabled with the option in octavia.conf:
[oslo_middleware]
enable_proxy_headers_parsing=True

Story: 2005105
Task: 29732
Change-Id: I276188530a83598ed75560f02ed9d80ce9afca2f

etc/octavia.conf

@@ -269,6 +269,10 @@
 # Topic (i.e. Queue) Name
 # topic = octavia_prov
 
+[oslo_middleware]
+# HTTPProxyToWSGI middleware enabled
+# enable_proxy_headers_parsing = False
+
 [house_keeping]
 # Interval in seconds to initiate spare amphora checks
 # spare_check_interval = 30

octavia/api/app.py

@@ -16,6 +16,7 @@ import keystonemiddleware.audit as audit_middleware
 from oslo_config import cfg
 from oslo_log import log as logging
 from oslo_middleware import cors
+from oslo_middleware import http_proxy_to_wsgi
 from oslo_middleware import request_id
 import pecan
 
@@ -83,6 +84,8 @@ def _wrap_app(app):
     if cfg.CONF.api_settings.auth_strategy == constants.KEYSTONE:
         app = keystone.SkippingAuthProtocol(app, {})
 
+    app = http_proxy_to_wsgi.HTTPProxyToWSGI(app)
+
     # This should be the last middleware in the list (which results in
     # it being the first in the middleware chain). This is to ensure
     # that any errors thrown by other middleware, such as an auth

releasenotes/notes/support-oslo_middleware-http_proxy_to_wsgi-928c6fc5ec3d421c.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Now supports ``oslo_middleware http_proxy_to_wsgi``, which will set up the
+    request URL correctly in the case that there is a proxy (for example, a
+    loadbalancer such as HAProxy) in front of the Octavia API. It is off by
+    default and can be enabled by setting ``enable_proxy_headers_parsing=True``
+    in the ``[oslo_middleware]`` section of ``octavia.conf``.