man dacs_auth_agent (8): DACS delegated authentication service

SYNOPSIS

dacs_auth_agent [m[blue]dacsoptionsm[][1]]

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 m[blue]dacs_authenticate(8)m[][2]). 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 m[blue]dacs_authenticate(8)m[][2], m[blue]dacs_auth_transfer(8)m[][3], m[blue]dacscred(1)m[][4], m[blue]dacscookie(1)m[][5], 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 m[blue]su(1)m[][6] 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 m[blue]standard CGI argumentsm[][7], 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 m[blue]dacs_authenticate(8)m[][2] service.

OPERATION

: This optional parameter is as described for the m[blue]dacs_authenticate(8)m[][2] service.

COOKIE_SYNTAX

: This optional parameter is as described for the m[blue]dacs_authenticate(8)m[][2] 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 m[blue]ADMIN_IDENTITYm[][8] will be returned only if the m[blue]AUTH_AGENT_ALLOW_ADMIN_IDENTITYm[][9] configuration directive has the value "yes". Refer to m[blue]dacs.conf(5)m[][10] for a description of these configuration directives.

A revocation test is always performed on the DACS identity; see m[blue]dacs.acls(5)m[][11] 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 m[blue]isprint(3)m[]

[12].

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 "[email protected]", which will become the mapped name (this example is apropos of mapping m[blue]OpenIDm[][13] names).

When configured, roles are obtained for USERNAME in the same way as is done for m[blue]dacs_authenticate(8)m[][2].

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 "[email protected]" 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 m[blue]dacs_auth_transfer(8)m[][3].

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.