DACS_AUTH_AGENT(8) | DACS Web Services and CGI | DACS_AUTH_AGENT(8)

## NAME

dacs_auth_agent — DACS delegated authentication service

## SYNOPSIS

`dacs_auth_agent` [`dacsoptions`]

## DESCRIPTION

This web service is part of the DACS suite.

The dacs_auth_agent web service is used to request DACS credentials outside of the usual DACS authentication procedure (see dacs_authenticate(8)). The client making the service request, whether a user agent or middleware, is considered to be an "agent" trusted by the jurisdiction that receives the request by virtue of having obtained DACS credentials and satisfying DACS access control rules that grant it access to this service. In other words, an agent simply requests credentials for a given identity from dacs_auth_agent and they are returned if an access control rule grants access and dacs_auth_agent is configured appropriately.

The agent's DACS credentials can be obtained through dacs_authenticate(8), dacs_auth_transfer(8), dacscred(1), dacscookie(1), or even dacs_auth_agent.

If the request is successful, credentials are returned to the client within an HTTP cookie. Credentials generated by this service can be distinguished from those created by one of the other methods.

### Security

Access control rules are responsible for expressing restrictions on the types of operations to be granted to various trusted agents. Access to this web service must not be granted without establishing and testing carefully crafted access control rules and appropriate configuration. By default, all access to this service is denied.

Much like Unix's su(1) command lets the superuser assume the Unix identity of any other user, this service provides a way for a privileged client to request credentials for a user known to the receiving jurisdiction. Any other credentials in the possession of the client remain in effect. Help desk personnel and system administrators can use this capability to assist users by temporarily impersonating a user without having to know the user's password, obtaining the user's client certificate, or following the user's usual authentication procedure.

The service can also be invoked to effectively import an identity that is recognized by the agent but possibly not known to the receiving jurisdiction. This provides a way to convert foreign credentials, whether from a non-DACS based system or a different DACS federation, into credentials understood by the federation of the receiving jurisdiction. It is only necessary for the agent to understand the foreign credentials; DACS never sees them.

Another use of this service is in conjunction with middleware that does its own authentication. Having authenticated a user, an application can ask dacs_auth_agent for DACS credentials for the user.

### Web Service Arguments

In addition to the standard CGI arguments, dacs_auth_agent understands the following CGI arguments:

`USERNAME`

  If present, the agent asserts that `USERNAME` is in some sense known to this jurisdiction.

`ALIEN_FEDERATION`

  If present, the agent asserts that `ALIEN_USERNAME`, which must be provided, is associated with the named external system. This can be any string comprised of characters allowed in a DACS username; presumably the agent and DACS jurisdiction have agreed on the name to use. This name, or a string mapped from it, will be incorporated into the resulting DACS username and credentials.

`ALIEN_USERNAME`

  If present, the `ALIEN_FEDERATION` argument must also be given. The agent asserts that the given name, relative to `ALIEN_FEDERATION`, has been authenticated. This can be any string comprised of characters allowed in a DACS username. This name, or a string mapped from it, will be incorporated into the resulting DACS username and credentials.

`DACS_JURISDICTION`

  This identifies the receiving jurisdiction.

`DACS_BROWSER`

  This optional parameter is as described for the dacs_authenticate(8) service.

`OPERATION`

  This optional parameter is as described for the dacs_authenticate(8) service.

`COOKIE_SYNTAX`

  This optional parameter is as described for the dacs_authenticate(8) service.

### Operation

There are two modes of operation. In `local mode`, the `USERNAME` argument is provided and is purported to be the DACS username of a user known to the receiving jurisdiction.

The second mode, called `alien mode`, is selected if both an `ALIEN_FEDERATION` argument and an `ALIEN_USERNAME` argument are present. It is an error if only one of these arguments is given, and the `USERNAME` is ignored. The mode checks that the `ALIEN_FEDERATION` and the `ALIEN_USERNAME` relative to it are satisfactory. This is done by requiring the `ALIEN_FEDERATION` to be recognized by the receiving jurisdiction; it may optionally be mapped to a different string. Similarly, the `ALIEN_USERNAME` argument must be recognized, relative to `ALIEN_FEDERATION` or the string mapped from it.

Credentials that have been designated as an ADMIN_IDENTITY will be returned only if the AUTH_AGENT_ALLOW_ADMIN_IDENTITY configuration directive has the value "`yes`". Refer to dacs.conf(5) for a description of these configuration directives.

A revocation test is always performed on the DACS identity; see dacs.acls(5) for a description of how authentication revocation works.

#### Local Mode

If the `USERNAME` argument is provided, it must consist of printable characters, as determined by isprint(3).

By default, dacs_auth_agent will blindly accept the trusted client's assertion that `USERNAME` is known to the receiving jurisdiction. An administrator can constrain `USERNAME`, however, and optionally map it into a replacement that is a valid DACS username.

If the virtual filestore item type "`auth_agent_local`" is configured, it is expected to name a file consisting of expressions, one per line (a continued line ends with a backslash). Each expression is evaluated in turn until one returns a non-empty string value; this value, which must be a syntactically correct DACS username, becomes the mapped username. An evaluation error is fatal. The value of the `USERNAME` argument is available to each expression as `${Expr::_}` (reminiscent of Perl's `$_` variable).

For example, consider the configuration directive:

    VFS "[auth_agent_local]dacs-fs:/usr/local/dacs/auth_agent_local_users"

and the file /usr/local/dacs/auth_agent_local_users, which contains:

    regsub(${Expr::_}, "^auggie doggie$", "auggie")
    regsub(${Expr::_}, "^julia$", "sara")
    strtr(regsub(${Expr::_}, \
        "\([^:]*\)://\([^.]*\)\\.\(.*\)", '${1}-${2}@${3}'), \
          "A-Z", "a-z")

If `USERNAME` is "`auggie doggie`", credentials will be issued for "`auggie`". If `USERNAME` is "`julia`", credentials will be issued for "`sara`". If `USERNAME` is "`https://Bob.Example.com`", the third expression will return the string "`https-bob@example.com`", which will become the mapped name (this example is apropos of mapping OpenID names).

When configured, roles are obtained for `USERNAME` in the same way as is done for dacs_authenticate(8).

#### Alien Mode

The alien mode of operation proceeds as follows:

1. It looks up `ALIEN_FEDERATION` using item type `auth_agent_federations`. When forming a key, the lookup operation will percent-encode any '`:`' and '`%`' characters in `ALIEN_FEDERATION`, so the same encoding is required for keys that appear in `auth_agent_federations`. If it is not found, authentication fails. If found, it may optionally have a value; that value will be used within the resulting DACS credentials instead of the `ALIEN_FEDERATION` argument. In any case, the resulting value must be valid for a DACS username.

2. It looks up `ALIEN_USERNAME` using an item type constructed by prepending the string "`auth_agent_federation_`" to the federation name derived during the previous step. When forming a key, the lookup operation will percent-encode any '`:`' and '`%`' characters in `ALIEN_USERNAME`, so the same encoding is required for stored keys. If it is not found, authentication fails. If found, it may optionally have a value; that value will be used within the resulting DACS credentials instead of the `ALIEN_USERNAME` argument. In any case, the resulting string must be valid for a DACS username.

3. A DACS username will be formed using the federation name and username strings derived in the previous steps.

## EXAMPLES

The following is an example of local mode operation. Assume the following configuration directive is in effect:

    VFS "[auth_agent_local]dacs-fs:/usr/local/dacs/auth_agent_local_users"

Also assume that the file /usr/local/dacs/auth_agent_local_users contains the expression:

    regsub(${Expr::_}, \
        "\([^:]*\)://\([^.]*\)\\.\(.*\)", '${1}-${2}@${3}')

If a request is made with `USERNAME` equal to "`http://Bob.Example.com`", new credentials will be issued for "`http-Bob@Example.com`" relative to the current jurisdiction.

The following is an example of alien mode operation. Assume the following configuration directives are in effect:

    VFS "[auth_agent_federations]dacs-kwv-fs:/usr/local/dacs/auth_agent_feds"
    VFS "[auth_agent_federation_mars]dacs-kwv-fs:/usr/local/dacs/auth_agent_fed_mars"

Also assume that the file /usr/local/dacs/auth_agent_feds consists of the line

    MARS:

and the file /usr/local/dacs/auth_agent_fed_mars consists of the line

    gazoo:

If a request is made with `ALIEN_FEDERATION` equal to "`MARS`" and `ALIEN_USERNAME` equal to "`gazoo`", the request will satisfy alien mode's rules of operation with the strings "`MARS`" and "`gazoo`" being used to form the DACS username relative to the current jurisdiction (`DACS_JURISDICTION`).

If instead `ALIEN_FEDERATION` were "`http://example.com`" and the file /usr/local/dacs/auth_agent_feds looked like:

    http%3A//example.com:example

then the string "`example`" would be used with "`gazoo`" to form the DACS username.

## DIAGNOSTICS

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

## NOTES

The word "`alien`" is used because it sounds cooler than "`foreign`" and is arguably easier to spell.

A superficially similar feature called "affiliated DACS federations", which provides single sign-on across federation boundaries, is sometimes a more appropriate solution; see dacs_auth_transfer(8).

## BUGS

It should be possible for keys that are matched against `USERNAME` to be regular expressions and for the corresponding replacement values to interpolate matched substrings.

## SEE ALSO

dacs_authenticate(8), dacs_auth_transfer(8), dacs_current_credentials(8), dacs_signout(8), dacs.exprs(5), dacscred(1), dacscookie(1).

## AUTHOR

Distributed Systems Software (www.dss.ca)

## COPYING

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

DACS Version 1.4.27b | 19-Mar-2012 | DACS_AUTH_AGENT(8)

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$Id: dacs_auth_agent.8.xml 2566 2012-03-02 16:56:19Z brachman $