Murano doesn't handle request properly if it is behind an SSL
termination proxy. In this case HTTP redirection and returned URLs
use http instead of https.
New middleware helps to handle the situation below properly. The purpose of the
SSLMiddleware is to update the wsgi.url_scheme environment variable of
the request with the value contained in an HTTP header that can be
configured in the configuration file (by default: 'X-Forwarded-Proto')
Closes-Bug: #1504610
Change-Id: Id7cfa1bce00c965b618a4f3e4ca2c915a57bbe52
8e01d101c7