Regex Tightening to Resolve URL Redirection Vulnerability

After a successful login, HUE allows redirection to an arbitrary site by modifying the site "<malicious.com>" in the URL: http://<my hue site>/accounts/login/?next=//<malicious.com>.

Since the attacker is allowed to fully control the name of the destination site, this could be used to mount a phishing attack against http://<my hue site>'s users, such as requiring the users to re-enter their credentials at the new site.

This patch tightens the redirect_whitelist configuration default value to "^(\/[a-zA-Z0-9]+.*|\/)$”, and limits all redirections to the same host where HUE is running by default to prevent phishing attacks.

https://issues.cloudera.org/browse/HUE-2485 partially addressed the URL redirection issue, but this further mitigates the risk.