SSL client certificates

By using SSL client certificates, you get automatically logged into SemanticScuttle without using a password or submitting a login form.

Any number of certificates can be registered with a user account, making it easy to login to the same installation from home and from work - without risking to use the same certificate on both machines.

Usage scenarios

The scenarios assume that the web server is configured properly to request client certificates.

Registering a certificate with an existing account

You already have an account and want to associate a SSL client certificate with it.

  1. Visit your profile page
  2. Click "Register current certificate to automatically login."

That's it. Now logout and click "Home". You will be logged in again automatically.

Registering a certificate with a new account

When you do not have an user account yet, just visit the registration page. Your email address will already be filled in, using the information from the SSL certificate.

Provide the rest of the data and submit the form. The certificate will automatically be associated to your account, and the user name will also be set for you.

Configuring your web server

Getting SSL certificates

You need both a server certificate for normal HTTPS mode, as well as a client certificate in your browser. is a good place to obtain both. You are of course free to generate your own certificate with i.e. openssl or buy a certificate from another certificate authority, but this is out of this document's scope.

Server certificate

First, generate a Certificate Signing Request with the CSR generator. Store the key file under


Use the the .csr file and the CAcert web interface to generate a signed certificate. Store it as


Now fetch both official CAcert certificates (root and class 3) and put both together into


Client certificate

CAcert also offers to create client certificates. You do not need a certificate sign request but just can create it on their web page.

After creation, you can simply install it in your browser by clicking on the appropriate link on the CAcert page.

Once you got the certificate installed in your browser, you can transfer it to other browsers by exporting it in the PKCS #12 format (with private key included) and importing it in any other browsers you use.

Apache configuration

To make use of SSL client certificates, you need to deliver SemanticScuttle via HTTPS.

Note that you can equip several virtual hosts with SSL certificates and keep them on the same, standard SSL port by using SNI - Server Name Indication.

A basic virtual host configuration with SSL looks like this:

<VirtualHost *:443>

    LogFormat "%V %h %l %u %t \"%r\" %s %b" vcommon
    CustomLog /var/log/apache2/access_log vcommon

    VirtualDocumentRoot /home/cweiske/Dev/html/hosts/
    <Directory "/home/cweiske/Dev/html/hosts/">
        AllowOverride all

    SSLEngine On
    SSLCertificateFile /etc/ssl/private/
    SSLCertificateKeyFile /etc/ssl/private/

    SSLCACertificateFile /etc/ssl/private/cacert-1and3.crt

Apart from that, you might need to enable the SSL module in your webserver, i.e. by executing

$ a2enmod ssl

Now that SSL works, you can configure your web server to request client certificates.


    SSLVerifyClient optional
    SSLVerifyDepth 1
    SSLOptions +StdEnvVars

There are several options you need to set:

SSLVerifyClient optional

You may choose optional or required here. optional asks the browser for a client certificate but accepts if the browser (the user) does choose not to send any certificate. This is the best option if you want to be able to login with and without a certificate.

Setting required makes the web server terminate the connection when no client certificate is sent by the browser. This option may be used when all users have their client certificate set.

SSLVerifyDepth 1

Your client certificate is signed by a certificate authority (CA), and your web server trusts the CA specified in SSLCACertificateFile. CA certificates itself may be signed by another authority, i.e. like

CAcert >> your own CA >> your client certificate

In this case, you have a higher depth. For most cases, 1 is enough.

SSLOptions +StdEnvVars

This makes your web server pass the SSL environment variables to PHP, so that SemanticScuttle can detect that a client certificate is available and read its data.

In case you need the complete certificate - which SemanticScuttle does not need - you have to add +ExportCertData to the line.

That's it. Restart your web server and visit your SemanticScuttle installation. Continue reading the Usage scenarios.