autologin — Convert an Apache identity to a DACS identity


autologin [dacsoptions]


This program is part of the DACS suite.

The autologin CGI program, in conjunction with appropriate Apache and DACS configuration, is used to automatically convert an identity already established by Apache into a DACS identity. After standard HTTP Basic or Digest Authentication (RFC 2617) has been performed successfully, autologin causes DACS credentials to be generated and returned. This capability lets DACS leverage any of Apache's existing authentication methods through simple configuration.

A user that has completed Basic or Digest Authentication (following a 401 Authorization Required response from the web server) invokes autologin. autologin generates credentials by constructing a request to dacs_authenticate(8). The value of the REMOTE_USER environment variable, as set by Apache, is used by dacs_authenticate to derive the DACS username.


This web service is deprecated in favour of the RFC 2617 capability built-in to DACS. For details, please refer to the HTTP Authentication section in dacs_acs(8).


autologin is not installed by default when DACS is built, in part because it can be a bit tricky to configure correctly and securely. Because this program is run during authentication processing, its file permissions must be set to prevent replacement or alteration by users other than a DACS administrator.


Only the standard dacsoptions command line arguments are recognized.

Web Service Arguments

autologin understands the following CGI arguments. All arguments are required unless otherwise indicated.


The path to the DACS configuration file that should be used to locate jurisdiction configuration information needed by dacs_authenticate.


When autologin is invoked as a result of DACS event handling, DACS_ERROR_URL is automatically passed by dacs_acs(8) and represents the original URL to which access was denied. In typical use, autologin is configured as the handler for a dacs_acs 902 error code (NO_AUTH, "Authentication by DACS is required"). autologin 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).


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


When autologin is invoked as a result of DACS event handling, DACS_JURISDICTION is automatically set by DACS to the name of the jurisdiction that received the request. By default, autologin generates credentials for the jurisdiction at which dacs_authenticate is invoked (specifically, DACS_JURISDICTION). This can be overridden by the DACS_SET_JURISDICTION parameter.


This optional argument explicitly names the jurisdiction in which autologin should generate credentials. DACS_SET_JURISDICTION overrides the value, if any, of DACS_JURISDICTION and must be the same as the jurisdiction in which autologin is deployed.


This is the URI identifying the jurisdiction in the DACS configuration file corresponding to the value specified in a DACS_JURISDICTION or DACS_SET_JURISDICTION argument. This argument is optional since the jurisdiction name can be used for this purpose.


This optional argument is useful for debugging. If the value of QUERY_STRING is exactly jump_dump_stdin, then the program will simply copy its standard input to the standard output as text/plain.


A typical use of autologin is to support coexistence on the same Web site of DACS-wrapped content, services. legacy applications, or content deployed under HTTP Basic or Digest Authentication. The following example illustrates configuration of Apache and DACS for the deployment under HTTP Basic Authentication of a web log application, Blogo. Blogo will be deployed within a DACS jurisdiction METALOGIC. The URI space of interest will be*.

In the Apache configuration file httpd.conf, a Location is defined for the Blogo application under Basic Authentication:

<Location /metalogic/blogo>
  AuthType Basic
  AuthName "FedDev"
  AuthUserFile /local/etc/auth-file
  Require valid-user
# Note: For Apache 2.4, instead use:
# Require dacs-authz

A Location under Basic Authentication also is defined where the autologin utility is deployed:

<Location /metalogic/dacs-native>
  AuthType Basic
  AuthName "FedDev"
  AuthUserFile /local/etc/auth-file
  Require valid-user
# Note: For Apache 2.4, instead use:
# Require dacs-authz

At the same time, other content in METALOGIC is protected by DACS:

<Location /metalogic/dev>
  Allow from all
  AuthType DACS
  AuthDACS dacs-acs
  Require valid-user
# Note: For Apache 2.4, instead use:
# Require dacs-authz


Basic Authentication cannot be specified in a subdirectory of a directory or location that has been configured for DACS access control. As above, DACS and Basic Authentication must be configured in separate locations.

In the DACS configuration file, dacs.conf, jurisdiction METALOGIC is configured as follows:

<Jurisdiction uri="">



<!-- Authenticate using Apache Basic/Digest Auth. -->
<Auth id="native">
URL ""
STYLE "native"
CONTROL "sufficient"



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

The preceding configuration results in the following behaviour. A user accessing Blogo directly ( is challenged to enter a valid username and password (with respect to the Apache accounts in /local/etc/auth-file). If the user subsequently accesses DACS content requiring DACS authentication but no DACS credentials are present:

  • The 902 event handler is invoked, resulting in a browser redirect to autologin.

  • The REMOTE_USER environment variable is present in the environment as a result of successful Basic Authentication.

  • autologin runs dacs_authenticate (as a command, not as a web service).

  • dacs_authenticate then invokes local_native_authenticate, which uses the value of REMOTE_USER as the USERNAME argument.

  • If authentication succeeds, DACS credentials for REMOTE_USER in jurisdiction METALOGIC 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 autologin by dacs_acs when the 902 handler was invoked and is forwarded to dacs_authenticate).

If the user accesses DACS content without first visiting the Blogo application, the 902 event handler fires, resulting in a browser redirect to autologin. Since autologin is itself behind Basic Authentication, the user will be prompted for a username and password. Once Basic Authentication succeeds, autologin is invoked with REMOTE_USER set (and therefore so is dacs_authenticate) and the process described above is repeated.

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

<a href="\

Following the link above results first in a Basic Authentication challenge and then sets DACS credentials in jurisdiction METALOGIC.


autologin cannot generate credentials in a jurisdiction other than the one in which autologin is deployed.

The behaviour of browsers with respect to the HTTP 401 Authorization status code may have undesired consequences. For example, browsers continually send username and password in any matching request. If a user does not exit the browser, this can result in DACS credentials automatically being regenerated long after their configured lifetime has expired. RFC 2617 provides no way for the server to "signout" a user, and neither do many browsers other than by ending the browser session or clearing browser history appropriately. This makes it inconvenient for a user to reauthenticate with respect to DACS using this technique.


The program exits 0 if successful, 1 if an error occurred.


dacs_authenticate(8) (in particular, the native authentication style), dacs_autologin_ssl(8), dacs_acs(8), dacs.conf(5)


Metalogic Software Corp. and Distributed Systems Software (


Copyright 2003-2018 Distributed Systems Software. See the LICENSE file that accompanies the distribution for licensing information.

DACS Version 1.4.50 21-Jul-2023 AUTOLOGIN(8)

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