By default, mod_wsgi filters out authentication requests that are used for logging in with our API. Any brand-new installations using Review Board 1.5.2 or higher should work, but if you're upgrading from an older install, you will need to add the following to your web server's configuration:
This would usually go right above your WSGIScriptAlias line.
Once you've added this, restart your web server and try again. If it still won't work, contact us on the discussion forum.