The SAML authentication object is initialized with a particular HTTP

host, and will reject any requests that come in with other hostnames.

We've run into a case with a user where they want to use a reverse proxy

for some users that give them a different hostname for the Review Board

server, and while their proxy can rewrite URLs in requests and content,

it's failing to handle the auth because of this. This change adds a step

to allow any hostname which is properly configured in the

ALLOWED_HOSTS setting to be passed through to the SAML library.

Ran unit tests.
Affected user reports that this solves their issue.