Using the X509 authentication source with SimpleSAMLphp

The authX509 module provides X509 authentication with certificate validation. For now there is only one authentication source:

• authX509userCert Validate against LDAP userCertificate attribute

More validation schemes (OCSP, CRL, local list) might be added later.

Configuring Apache

This module assumes that the server requests a client certificate, and stores it in the environment variable SSL_CLIENT_CERT. This can be achieved with such a configuration:

    SSLEngine on
    SSLCertificateFile /etc/openssl/certs/server.crt
    SSLCertificateKeyFile /etc/openssl/private/server.key
    SSLCACertificateFile /etc/openssl/certs/ca.crt
    SSLVerifyClient require
    SSLVerifyDepth 2
    SSLOptions +ExportCertData

Note that SSLVerifyClient can be set to optional if you want to support both certificate and plain login authentication at the same time (more on this later).

If your server or your client (or both!) have TLS renegotiation disabled as a workaround for CVE-2009-3555, then the configuration directive above must not appear in a <Directory>, <Location>, or in a name-based <VirtualHost>. You can only use them server-wide, or in <VirtualHost>s with different IP address/port combinations.

Setting up the authX509 module

The first thing you need to do is to enable the module: in config.php , search for the module.enable key and set authX509 to true:

    'module.enable' => [
         'authX509' => true,
         …
    ],

Then you must add it as an authentication source. Here is an example authsources.php entry:

    'x509' => [
        'authX509:X509userCert',
        'backend' => 'ldap',
        'authX509:x509attributes' => ['UID' => 'uid'],
        'authX509:ldapusercert' => ['userCertificate;binary'],
    ],

    'ldap' => [
        'connection_string' => 'ldaps://ldap.example.net',
        'encryption' => 'ssl',
        'attributes' => ['cn', 'uid', 'mail', 'ou', 'sn'],
        'search.enable' => true,
        'search.attributes' => ['uid', 'mail'],
        'search.base' => ['dc=example,dc=net'],
    ],

The configuration is the same as for the LDAP module, except for two options:

• x509attributes is used to map a certificate subject attribute to an LDAP attribute. It is used to find the certificate owner in LDAP from the certificate subject. If multiple mappings are provided, any mapping will match (this is a logical OR). Default is array('UID' => 'uid').
• ldapusercert the LDAP attribute in which the user certificate will be found. Default is userCertificate;binary. This can be set to NULL to avoid looking up the certificate in LDAP.

Uploading certificate in LDAP

Certificates are usually stored in LDAP as DER, in binary. Here is how to convert from PEM to DER:

    openssl x509 -in cert.pem -inform PEM -outform DER -out cert.der

Here is some LDIF to upload the certificate in the directory:

dn: uid=jdoe,dc=example,dc=net
changetype: modify
add: userCertificate;binary
userCertificate;binary:< file:cert.der
-

Supporting both certificate and login authentication

In your Apache configuration, set SSLVerifyClient to optional. Then you can hack your metadata/saml20-idp-hosted.php file that way:

    $auth_source = empty($_SERVER['SSL_CLIENT_CERT']) ? 'ldap' : 'x509';
    $metadata = array(
        '__DYNAMIC:1__' => [
            'host'          =>      '__DEFAULT__',
            'privatekey'    =>      'server.key',
            'certificate'   =>      'server.crt',
            'auth'          =>       $auth_source,
            'authority'     =>      'login',
            'userid.attribute' =>   'uid',
            'logouttype'    =>      'iframe',
            'attributes.NameFormat' => 'urn:oasis:names:tc:SAML:2.0:attrname-format:uri',
    ];

Checking certificate expiry

To issue warnings to users whose certificate is about to expire, configure an authproc filter.

Example:

     10 => [
         'class' => 'authX509:ExpiryWarning',
         'warndaysbefore' => 30,
         'renewurl' => 'https://myca.com/renew',
     ],

Parameter warndaysbefore specifies the number of days the user's certificate needs to be valid before a warning is issued. The default is 30.

Parameter renewurl specifies the URL of your Certification Authority. If specified, the user is suggested to renew the certificate immediately.