One of the most secure ways of user authentication- is the PKI authentication. A lot of modern systems support this method and everything works nice and smoothly (almost everything - details in the my next post). But, as usually, in real big enterprise you have a dilemma: you need the strongest authentication but you have a lot of legacy systems (or it takes ages to get changes in authentication method from vendor).
The best way (IMHO) to resolve this problem is to use mutual ssl on certificates.
SSL will terminate on reverse proxy server in front of your Business Application Server inside the high secure network zone . So, here the scheme:
It looks really easy, isn't it?
How it works:
1. Each user has his own certificate and private key. It could be located on smart card, token or inside OS key storage.
2. User's browser must be configured to use this certificate for authentication (It's easy - just import it in browser or point it to OS key storage)
3. User must connect to revers proxy server (ssl termination point) for getting access to Business Application Server.
4. Revers proxy server checks validity of user's certificate and some certificate's fields (if you need to restrict access to only some users groups) like OU, CN or "extended key usage" and establish mutual ssl connection.
5. Revers proxy server offloads ssl and make direct connection over http (or non-mutual ssl connection) to your business application server.
6. Business application server authenticate user and authorised them by user/password pair.
The key point of this scheme is the Revers Proxy Server with ssl offloading feature (May be the better name for it - Secure Application Gateway).
How this servers looks like?
1. Open Source:
Any *nix + Apache web server with mod_proxy and mod_ssl + some changes in Apache config for certificate verification.
2. Load balancer or Web Application firewall from your favorite vendor. I have tested this on F5 BigIP and everything works perfectly.
Almost forget. You will get a lot of users' web request logging possibilities during implementation of this scheme. So you can easily control users' activity within business application server.
That's all folks. Stay secure.