dacs_autologin_ssl — use an SSL client certificate to automatically obtain DACS credentials


dacs_autologin_ssl [dacsoptions]


This program is part of the DACS suite.

The dacs_autologin_ssl CGI program, in conjunction with appropriate DACS configuration and a valid SSL client certificate, can be used for user-transparent DACS authentication. A user is not prompted for a username or password, and no user-visible sign-on procedure takes place.

At present, the program merely acts as glue to indirectly invoke dacs_authenticate(8). Any valid X.509 certificate can be used for this purpose, including a self-signed certificate. Please refer to the OpenSSL documentation for additional information about certificates.

This program can be used to automatically and transparently authenticate a user that has been issued an SSL client certificate. When an unauthenticated user is denied access to a DACS-wrapped resource, she can be automatically authenticated and redirected back to the resource without any user input or action. This assumes that the client certificate is sent automatically by the browser and that no additional user prompting is needed by the authenticating jurisdiction. For redirection to the original resource to work properly. the original request must have used the GET method.


The cert style of authentication must be configured when dacs_autologin_ssl is being used as described. See dacs_authenticate(8).


Only the standard dacsoptions command line arguments are recognized.

Web Service Arguments

dasc_autologin_ssl understands the following CGI arguments.


When dacs_autologin_ssl is invoked as a result of DACS event handling, DACS_ERROR_URL is automatically passed to it by dacs_acs(8) and represents the original URL to which access was denied. In typical use, dacs_autologin_ssl is configured as the handler for a dacs_acs 902 error code (NO_AUTH, "Authentication by DACS is required"). dacs_autologin_ssl then invokes dacs_authenticate. If DACS authentication is successful, dacs_authenticate ordinarily issues a browser redirect to the value of DACS_ERROR_URL and a cookie bearing the credentials are set in the browser (but see the NOREDIRECT argument). This argument is optional; if not provided, the jurisdiction's configured post-authentication action will occur.


If this optional argument is present (its value is immaterial), dacs_autologin_ssl instructs dacs_authenticate to not issue a browser redirect to the value of DACS_ERROR_URL.


If this optional argument is present, it gives the name of the jurisdiction at which authentication should take place. By default, dacs_authenticate is invoked at the same jurisdiction as dacs_autologin_ssl.


This optional argument explicitly names the attribute in the certificate from which to set USERNAME. The default value is SSL_CLIENT_S_DN_CN. It is an error if the specified attribute name does not exist. Giving the value of CERT_NAME_ATTR as the empty string results in the empty string being passed as the value of USERNAME.


A typical use of dacs_autologin_ssl is to transparently authenticate a user via his SSL client certificate.

In the DACS configuration file, dacs.conf, jurisdiction EXAMPLE is configured as follows (this excerpt from a configuration file uses fictitious domain names):

<Jurisdiction uri="example.com">


ACS_ERROR_HANDLER "NO_AUTH https://example.com/cgi-bin/dacs/dacs_autologin_ssl"

<!-- Authenticate using an SSL certificate. -->
<Auth id="cert">
URL "https://example.com/cgi-bin/dacs/local_cert_authenticate"
STYLE "cert"
CONTROL "sufficient"
CERT_CA_PATH "/usr/local/apache2.2/conf/ssl.crt"


Assume the following access control rule applies to the request:

<acl_rule status="enabled">
    <service url_pattern='/foo.html'/>

  <rule order="allow,deny">

The preceding configuration results in the following behaviour. An unauthenticated user accessing foo.html (https://example.com/foo.html) is denied access because the rule governing that web page tests for authentication and no credentials are sent with the request. As a result, the ACS_ERROR_HANDLER directive causes the user to be redirected to dacs_autologin_ssl, which redirects the user to dacs_authenticate, passing arguments as necessary.

dacs_authenticate then invokes local_cert_authenticate, passing it the client's certificate. The certificate is validated and a username is extracted from it and mapped to a valid DACS username.

If authentication succeeds, DACS credentials for the jurisdiction EXAMPLE are generated. These credentials are returned to the browser within a cookie and the browser is redirected to the value of DACS_ERROR_URL (recall that DACS_ERROR_URL was passed to dacs_autologin_ssl by dacs_acs when the 902 handler was invoked and was forwarded to dacs_authenticate). In this example the user is redirected to https://example.com/foo.html. Given the rule above, this time the user's request for foo.html will be granted.

dacs_autologin_ssl may also be used as the target of an explicit authentication link. For example:

<a href="https://example.com/cgi-bin/dacs/dacs_autologin_ssl?\

Following the link should result in the user being authenticated and redirected to the specified URL.


The program exits 0 if everything was fine, 1 if an error occurred.


dacs_authenticate(8), dacs_acs(8), dacs.conf(5), autologin(8)


Distributed Systems Software (www.dss.ca)


Copyright 2003-2012 Distributed Systems Software. See the LICENSE file that accompanies the distribution for licensing information.

DACS Version 1.4.38a 23-Nov-2016 DACS_AUTOLOGIN_SSL(8)

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$Id: dacs_autologin_ssl.8.xml 2563 2012-02-07 22:40:41Z brachman $