This is a simple example how to setup TLS Certificate Authentication for your online services. The example is based on nginx and WSGI but should work also with an FCGI backend with PHP.

Using tlsauth you can authenticate your users based on certificates instead of passwords. In fact you don’t have to store neither the usernames, their email addresses nor their nicks, it is all contained in the Client certificate that is stored and presented by the user. You can be sure, unless your signing key is compromised, noone else can create valid certificates but you. This eliminates the need to remember passwords and prohibits password bruteforcing. Using nginx, you can even display totally different content depending if an request is authenticated or not, routing unauthenticated users to static html for example while authenticated users having access to some dynamic content.

I don’t want to scare you but this is essentially a self-signed CA, it provides all the neccessary basic tools to make this hassle-free. Your users only need to go through a registration procedure and then they could enjoy seamless single-sign-on to all your services, never being asked for a password again.

./tlsauth.py root-ca createca http://localhost/crl.pem "Example CA" [email protected]

./tlsauth.py sub-ca createca http://localhost/client-crl.pem "hostname client CA" [email protected] root-ca

./tlsauth.py root-ca newcsr localhost root@localhost >server.key

./tlsauth.py sign <server.key >server.pem

It is important to remove and store the root CA private key in a safe offline location, as it can be used to mount a MITM attack against all users, who trust this key. You need this key in 1 year, when you need to renew your client CA certificate (per default it’s only valid for one year!)

mv root-ca/private/root.key <private and save location>

server {
    listen        443;
    ssl on;
    server_name localhost;

    ssl_certificate      <pathto>/tlsauth/server.cert;
    ssl_certificate_key  <pathto>/tlsauth/server.key;
    ssl_client_certificate <pathto>/tlsauth/sub-ca/public/root.pem;
    ssl_verify_client optional;

    location / {
       include uwsgi_params;
       uwsgi_param verified $ssl_client_verify;
       uwsgi_param dn $ssl_client_s_dn;
       if ( $ssl_client_verify = "SUCCESS") {
          uwsgi_pass 127.0.0.1:8080;
       }
       try_files $uri $uri/ /index.html;
    }
}

don’t forget to restart nginx.

Now if users have a proper client cert installed the environment of the WSGI application will contain the variables ‘verified’ and ‘dn’ variables set accordingly.

There’s a bundled demo, to try it out:

edit flask-demo/tlsdemo_wsgi.py

virtualenv --distribute env
source env/bin/activate
pip install Flask uwsgi

basedir=$PWD
env/bin/uwsgi --socket 127.0.0.1:8080 --chdir $basedir/flask-demo -pp $basedir -w tlsdemo_wsgi -p 1 --virtualenv $basedir/env

How to create a proper Client certificate.

./tlsauth.py root-ca newcsr joe joe@localhost >joe.key

send the resulting “user.csr” to the CA for signing. In this case you are both, but in a normal case this step is done by arbitrary users who send this csr file during the registration process to the site.

Store user.key away somewhere safe offline, you’ll need it later once more.

./tlsauth.py root-ca sign <joe.key >joe.cert

CA sends back the signed ‘user.cert” to the sender. As a convenience feature also the root CA cert should be sent to the user, so he can import this also in his CA store.

Using the returned cert from the CA we convert it together with the secret key part to a PKCS#12

./tlsauth.py root-ca p12 joe.key <joe.cert >joe.p12

This asks for a passphrase which is needed only once when importing into the browser.

1. Using the menu open the Preferences dialog.
2. Select the Advanced toolbar icon
3. click on the “View certificates” button
4. On the “Authorities” tab click on the Import button and import the root CA cert (this must be supplied by the CA to you).
5. on the “Your Certificates” tab click on the “Import” button and load the file “user.cert.p12”

if everything went ok the new certificate should appear under the “Your Certificates” tab

Store away private key in joe.key again together with the pkcs12 cert joe.p12 in a safe offline location (maybe your backup?), if you reinstall your browser you want to import user.cert.p12 back into it again.

If you now surf to https://localhost with this firefox, the flask application should report back your distinguished name. If you browse to this location with another browser which lacks this certificate you will probably see the default nginx installation html page.

see test.py

Fixed dangerously exposed Root CA key, by introducing a sub CA only for signing the client authentication keys, and thus eliminating the chance for a MITM attack in case the Root CA gets compromised.