-# Copyright 1999-2000, The OpenLDAP Foundation, All Rights Reserved.
+# Copyright 1999-2003, The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.
H1: Using SASL
-OpenLDAP clients and servers are capable of providing authentication
-via the {{TERM[expand]SASL}} ({{TERM:SASL}}) system, which is
-explained in {{REF:RFC2222}}. There are several industry standard
-authentication mechanisms that can be used with SASL, including
-Kerberos V4, GSSAPI, and some of the Digest mechanisms. The standard
-client tools provided with OpenLDAP, such as {{ldapsearch}}(1) and
-{{ldapmodify}}(1), will by default attempt to authenticate the user
-to the {{slapd}}(8) server using SASL. Basic authentication service
-can be set up by the LDAP administrator with a few steps, allowing
-users to be authenticated to the slapd server as their LDAP entry.
-With a few extra steps, some users and services can be allowed to
-exploit SASL's authorization feature, allowing them to authenticate
-themselves and then switch their identity to that of another user
-or service.
-
-Note that in the following text the term "{{user}}" is used to
-describe a person who is connecting to the LDAP server via a client
-program, such as {{ldapsearch}}(1). The term can also be used to
-describe a computer program that runs itself and accesses the LDAP
-database, such as a sendmail program or a nightly update program
-run out of cron. Thus {{"user"}} refers to any computer process
-connecting to the LDAP server, whether or not it has a human
-monitoring it.
-
-H2: Security Considerations
+OpenLDAP clients and servers are capable of authenticating via the
+{{TERM[expand]SASL}} ({{TERM:SASL}}) framework, which is detailed
+in {{REF:RFC2222}}. This chapter describes how to make use of
+SASL in OpenLDAP.
+
+There are several industry standard authentication mechanisms that
+can be used with SASL, including {{TERM:Kerberos}} V4, {{TERM:GSSAPI}},
+and DIGEST-MD. The standard client tools provided with OpenLDAP,
+such as {{ldapsearch}}(1) and {{ldapmodify}}(1), will by default
+attempt to authenticate the user to the {{slapd}}(8) server using
+SASL. Basic authentication service can be set up by the LDAP
+administrator with a few steps, allowing users to be authenticated
+to the slapd server as their LDAP entry. With a few extra steps,
+some users and services can be allowed to exploit SASL's proxy
+authorization feature, allowing them to authenticate themselves and
+then switch their identity to that of another user or service.
+
+This chapter assumes you have read {{Cyrus SASL for System
+Administrators}}, provided with the {{PRD:Cyrus}} {{PRD:SASL}}
+package (in {{FILE:doc/sysadmin.html}}) and have a working Cyrus
+SASL installation. You should use the Cyrus SASL {{EX:sample_client}}
+and {{EX:sample_server}} to test your SASL installation before
+attempting to make use of it in OpenLDAP.
+
+Note that in the following text the term {{user}} is used to describe
+a person or application entity who is connecting to the LDAP server
+via an LDAP client, such as {{ldapsearch}}(1). That is, the term
+{{user}} not only applies to both an individual using an LDAP client,
+but to an application entity which issues LDAP client operations
+without direct user control. For example, an e-mail server which
+uses LDAP operations to access information held in an LDAP server
+is an application entity.
+
+
+H2: SASL Security Considerations
SASL offers many different authentication mechanisms. This section
-breifly outlines security considerations.
+briefly outlines security considerations.
-Some mechanisms, such as PLAIN and LOGIN, offer no security over
+Some mechanisms, such as PLAIN and LOGIN, offer no greater security over
LDAP "simple" authentication. Like "simple" authentication, such
mechanisms should not be used unless you have adequate security
-protections in place. It is recommended that these mechanism be
+protections in place. It is recommended that these mechanisms be
used only in conjunction with {{TERM[expand]TLS}} (TLS). Use of
PLAIN and LOGIN are not discussed further in this document.
The DIGEST-MD5 mechanism is the mandatory-to-implement authentication
mechanism for LDAPv3. Though DIGEST-MD5 is not a strong authentication
mechanism in comparison with trusted third party authentication
-systems, it does offer significant protections against a number of
-attacks. Unlike the CRAM-MD5 mechanism, it prevents chosen plaintext
-attacks. DIGEST-MD5 is favored over weaker and even more dangerous
-use of plaintext password mechanisms. The CRAM-MD5 mechanism is
-deprecated in favor of DIGEST-MD5.
-
-# Use of DIGEST-MD5 is discussed below.
-
-The KERBEROS_V4 mechanism utilizes Kerberos IV services to provide
-secure authentication services. There are also GSSAPI based
-mechanisms which utilize Kerberos V. Kerberos is viewed as a
-secure, distributed authentication system.
-Use of KERBEROS_V4 is discussed below.
-#Use of KERBEROS_V4 and GSSAPI are discussed below.
+systems (such as Kerberos or public key systems), yet it does offer
+significant protections against a number of attacks. Unlike the
+CRAM-MD5 mechanism, it prevents chosen plaintext attacks. DIGEST-MD5
+is favored over the weaker and even more dangerous use of plaintext
+password mechanisms. The CRAM-MD5 mechanism is deprecated in favor
+of DIGEST-MD5. Use of {{SECT:DIGEST-MD5}} is discussed below.
+
+The KERBEROS_V4 mechanism utilizes Kerberos IV to provide secure
+authentication services. There is also a GSSAPI based mechanism
+which is generally used in conjunction with Kerberos V. Kerberos
+is viewed as a secure, distributed authentication system suitable
+for both small and large enterprises. Use of {{SECT:KERBEROS_V4}}
+and {{SECT:GSSAPI}} are discussed below.
The EXTERNAL mechanism utilizes authentication services provided
by lower level network services such as {{TERM:TLS}} (TLS). When
-used in conjunction with TLS X.509-based public key technology,
-EXTERNAL offers strong authentication.
-#Use of EXTERNAL is discussed in the TLS chapter.
+used in conjunction with {{TERM:TLS}} {{TERM:X.509}}-based public
+key technology, EXTERNAL offers strong authentication. Use of
+EXTERNAL is discussed in the {{SECT:Using TLS}} chapter.
There are other strong authentication mechanisms to choose from,
including OTP (one time passwords) and SRP (secure remote passwords).
H2: SASL Authentication
-Getting basic SASL authentication running involves a few steps. The
-first step configures your slapd server environment so
+Getting basic SASL authentication running involves a few steps.
+The first step configures your slapd server environment so
that it can communicate with client programs using the security
system in place at your site. This usually involves setting up a
service key, a public key, or other form of secret. The second step
V4 as an example mechanism. The steps necessary for your site's
authentication mechanism will be similar, but a guide to every
mechanism available under SASL is beyond the scope of this chapter.
-The next section after that describes the second step of mapping
-authentication identities to DN's.
-
+The second step is described in the section
+{{SECT:Mapping Authentication identities to LDAP entries}}.
-H3: Kerberos V4
+H3: KERBEROS_V4
This section describes the use of the SASL KERBEROS_V4 mechanism
with OpenLDAP. It will be assumed that you are familiar with the
-workings of Kerberos V4 security system, and that your site has
-either Kerberos V4 deployed. Your users should be familiar with
-authentication policy, are aware of how to receive credentials in
+workings of the Kerberos IV security system, and that your site has
+Kerberos IV deployed. Your users should be familiar with
+authentication policy, how to receive credentials in
a Kerberos ticket cache, and how to refresh expired credentials.
Client programs will need to be able to obtain a session key for
programs will be obtaining an "ldap" service ticket with the user's
ticket granting ticket (TGT), with the instance of the ticket
matching the hostname of the OpenLDAP server. For example, if your
-realm is named EXAMPLE.COM and the slapd server is running on the
-host named directory.example.com, the /etc/srvtab file on the server
-will have a service key
+realm is named {{EX:EXAMPLE.COM}} and the slapd server is running
+on the host named {{EX:directory.example.com}}, the {{FILE:/etc/srvtab}}
+file on the server will have a service key
> ldap.directory@EXAMPLE.COM
-When a LDAP client is authenticating a user to the directory using
+When an LDAP client is authenticating a user to the directory using
the KERBEROS_IV mechanism, it will request a session key for that
same principal, either from the ticket cache or by obtaining a new
one from the Kerberos server. This will require the TGT to be
> ldap_sasl_interactive_bind_s: Local error
When the service ticket is obtained, it will be passed to the LDAP
-server as proof of the user's identity. The server will take the
-user's username and realm out of the service ticket using SASL
+server as proof of the user's identity. The server will extract
+the identity and realm out of the service ticket using SASL
library calls, and convert them into an {{authentication request
DN}} of the form
-> uid=<username>,cn=<realm>,cn=<mechanism>,cn=authzid
+> uid=<username>,cn=<realm>,cn=<mechanism>,cn=auth
So in our above example, if the user's name were "adamson", the
authentication request DN would be:
-> uid=ADAMSON,cn=EXAMPLE.COM,cn=KERBEROS_V4,cn=AUTHZID
+> uid=adamsom,cn=example.com,cn=kerberos_v4,cn=auth
This authentication request DN by itself could be placed into ACL's
and {{EX:groupOfNames}} "member" attributes, since it is of legitimate
-LDAP DN format. The next section, however, tells how to map that
+LDAP DN format. The section
+{{SECT:Mapping Authentication identities to LDAP entries}},
+however, tells how to map that
DN into the DN of a person's own LDAP entry.
Also note that this example, being for Kerberos, shows the <realm>
portion of the DN being filled in with the Kerberos realm of the
-company. Several other authentication mechanisms do not emply the
+company. Several other authentication mechanisms do not employ the
concept of a realm, so the ",cn=<realm>" portion of the authentication
request DN would not appear.
+H3: GSSAPI
+
+This section describes the use of the SASL GSSAPI mechanism and
+Kerberos V with OpenLDAP. Since Kerberos V is being used, the
+information is very similar to the previous section. It will be
+assumed that you have Kerberos V deployed, you are familiar with
+the operation of the system, and that your users are trained in its
+use. This section also assumes you have familiarized yourself with
+the use of the GSSAPI mechanism by reading {{Configuring GSSAPI and
+Cyrus SASL}} (provided with Cyrus SASL in the {{FILE:doc/gssapi}}
+file) and successfully experimented with the Cyrus provided
+{{EX:sample_server}} and {{EX:sample_client}} applications. General
+information about Kerberos is available at
+{{URL:http://web.mit.edu/kerberos/www/}}.
+
+To use the GSSAPI mechanism with {{slapd}}(8) one must create a service
+key with a principal for {{ldap}} service within the realm for the host
+on which the service runs. For example, if you run {{slapd}} on
+{{EX:directory.example.com}} and your realm is {{EX:EXAMPLE.COM}},
+you need to create a service key with the principal:
+
+> ldap/directory.example.com@EXAMPLE.COM
+
+When {{slapd}}(8) runs, it must have access to this key. This is
+generally done by placing the key into a keytab, such as
+{{FILE:/etc/krb5.keytab}}.
+
+To use the GSSAPI mechanism to authenticate to the directory, the
+user obtains a Ticket Granting Ticket (TGT) prior to running the
+LDAP client. When using OpenLDAP client tools, the user may mandate
+use of the GSSAPI mechanism by specifying {{EX:-Y GSSAPI}} as a
+command option.
+
+For the purposes of authentication and authorization, {{slapd}}(8)
+associates a non-mapped authentication request DN of the form:
+
+> uid=<principal>,cn=<realm>,cn=gssapi,cn=auth
+
+Continuing our example, a user
+with the Kerberos principal {{EX:kurt@EXAMPLE.COM}} would have
+the associated DN:
+
+> uid=kurt,cn=example.com,cn=gssapi,cn=auth
+
+and the principal {{EX:ursula@FOREIGN.REALM}} would have the
+associated DN:
+
+> uid=ursula,cn=foreign.realm,cn=gssapi,cn=auth
+
+
+H3: DIGEST-MD5
+
+This section describes the use of the SASL DIGEST-MD5 mechanism using
+secrets stored either in the directory itself or in Cyrus SASL's own
+database. DIGEST-MD5 relies on the client and the server sharing a
+"secret", usually a password. The server generates a challenge and the
+client a response proving that it knows the shared secret. This is much
+more secure than simply sending the secret over the wire.
+
+Cyrus SASL supports several shared-secret mechanisms. To do this, it
+needs access to the plaintext password (unlike mechanisms which pass
+plaintext passwords over the wire, where the server can store a hashed
+version of the password).
+
+Secret passwords are normally stored in Cyrus SASL's own {{sasldb}}
+database, but if OpenLDAP has been compiled with Cyrus SASL 2.1 it is
+possible to store the secrets in the LDAP database itself. With Cyrus
+SASL 1.5, secrets may only be stored in the {{sasldb}}. In either
+case it is very important to apply file access controls and LDAP access
+controls to prevent exposure of the passwords.
+
+The configuration and commands discussed in this section assume the use
+of Cyrus SASL 2.1. If you are using version 1.5 then certain features
+will not be available, and the command names will not have the trailing
+digit "2".
+
+To use secrets stored in {{sasldb}}, simply add users with the
+{{saslpasswd2}} command:
+
+> saslpasswd2 -c <username>
+
+The passwords for such users must be managed with the {{saslpasswd2}}
+command.
+
+To use secrets stored in the LDAP directory, place plaintext passwords
+in the {{EX:userPassword}} attribute. It will be necessary to add an
+option to {{EX:slapd.conf}} to make sure that passwords changed through
+LDAP are stored in plaintext:
+
+> password-hash {CLEARTEXT}
+
+Passwords stored in this way can be managed either with {{EX:ldappasswd}}
+or by simply modifying the {{EX:userPassword}} attribute.
+
+Wherever the passwords are stored, a mapping will be needed from SASL
+authentication IDs to regular DNs. The DIGEST-MD5 mechanism produces
+authentication IDs of the form:
+
+> uid=<username>,cn=<realm>,cn=digest-md5,cn=auth
+
+NOTE that if the default realm is used, the realm name is omitted from
+the ID, giving:
+
+> uid=<username>,cn=digest-md5,cn=auth
+
+See {{SECT: Mapping Authentication identities to LDAP entries}} below
+for information on mapping such IDs to DNs.
+
+With suitable mappings in place, users can specify SASL IDs when
+performing LDAP operations, and the password stored in {{sasldb}} or in
+the directory itself will be used to verify the authentication.
+For example, the user identified by the directory entry:
+
+> dn: cn=Andrew Findlay+uid=u000997,dc=example,dc=com
+> objectclass: inetOrgPerson
+> objectclass: person
+> sn: Findlay
+> uid: u000997
+> userPassword: secret
+
+can issue commands of the form:
+
+> ldapsearch -U u000997 -b dc=example,dc=com 'cn=andrew*'
+
+or can specify the realm explicitly:
+
+> ldapsearch -U u000997@myrealm -b dc=example,dc=com 'cn=andrew*'
+
+If several SASL mechanisms are supported at your site, it may be
+necessary to specify which one to use, e.g.:
+
+> ldapsearch -Y DIGEST-MD5 -U u000997 -b dc=example,dc=com 'cn=andrew*'
+
+
+Note: in each of the above cases, no authorization identity (e.g.
+{{EX:-X}}) was provided. Unless you are attempting
+{{SECT:SASL Proxy Authorization}}, no authorization identity should
+be specified. The server will infer an authorization identity from
+authentication identity (as described below).
+
+
H3: Mapping Authentication identities to LDAP entries
The authentication mechanism in the slapd server will use SASL
library calls to obtain the authenticated user's "username", based
on whatever underlying authentication mechanism was used. This
username is in the namespace of the authentication mechanism, and
-not in the LDAP namespace. As stated in the section above, that
+not in the LDAP namespace. As stated in the sections above, that
username is reformatted into an authentication request DN of the
form
-> uid=<username>,cn=<realm>,cn=<mechanism>,cn=authzid
+> uid=<username>,cn=<realm>,cn=<mechanism>,cn=auth
or
-> uid=<username>,cn=<mechanism>,cn=authzid
+> uid=<username>,cn=<mechanism>,cn=auth
depending on whether or not <mechanism> employs the concept of
-"realms".
+"realms". Note also that the realm part will be omitted if the default
+realm was used in the authentication.
It is not intended that you should add LDAP entries of the above
form to your LDAP database. Chances are you have an LDAP entry for
each of the people that will be authenticating to LDAP, laid out
-in your directory tree, and the tree does not start at cn=authzid.
+in your directory tree, and the tree does not start at cn=auth.
But if your site has a clear mapping between the "username" and an
LDAP entry for the person, you will be able to configure your LDAP
-server to automatically map a user's authentication username to
-their {{authentication DN.}}
+server to automatically map a authentication request DN to the
+user's {{authentication DN}}.
+
+Note: it is not required that the authentication request DN nor the
+user's authentication DN resulting from the mapping refer to an
+entry held in the directory. However, additional capabilities
+become available (see below).
The LDAP administrator will need to tell the slapd server how to
map an authentication request DN to a user's authentication DN.
-This is done by adding one or more {{EX:saslRegexp}} directives to
+This is done by adding one or more {{EX:sasl-regexp}} directives to
the {{slapd.conf}}(5) file. This directive takes two arguments:
-> saslRegexp <search pattern> <replacement pattern>
+> sasl-regexp <search pattern> <replacement pattern>
The authentication request DN is compared to the search pattern
using the regular expression functions {{regcomp}}() and {{regexec}}(),
and if it matches, it is rewritten as the replacement pattern. If
-there are multiple {{EX:saslRegexp}} directives, only the first
+there are multiple {{EX:sasl-regexp}} directives, only the first
whose search pattern matches the authentication identity is used.
The string that is output from the replacement pattern should be
the authentication DN of the user, in a legitimate LDAP DN format.
characters listed in {{regexec}}(3C). The main characters of note
are dot ".", asterisk "*", and the open and close parenthesis "("
and ")". Essentially, the dot matches any character, the asterisk
-matches one or more characters, and terms in parenthesis are
+allows zero or more repeats of the immediately preceding character or
+pattern, and terms in parenthesis are
remembered for the replacement pattern.
The replacement pattern will produce the final authentication DN
matched a string in parenthesis in the search pattern is stored in
the variable "$1". That variable "$1" can appear in the replacement
pattern, and will be replaced by the string from the authentication
-request DN. If there were multiple sets of parenthesis in the search
+request DN. If there were multiple sets of parentheses in the search
pattern, the variables $2, $3, etc are used.
For example, suppose the user's authentication identity is written
as the DN string
-> uid=ADAMSON,cn=EXAMPLE.COM,cn=KERBEROS_V4,cn=AUTHZID
+> uid=adamson,cn=example.com,cn=kerberos_v4,cn=auth
and the user's actual LDAP entry is
-> uid=ADAMSON,ou=PERSON,dc=EXAMPLE,dc=COM
+> uid=adamson,ou=person,dc=example,dc=com
-The {{EX:saslRegexp}} directive in {{slapd.conf}}(5) could be
+The {{EX:sasl-regexp}} directive in {{slapd.conf}}(5) could be
written
-> saslRegexp
-> uid=(.*),cn=example.com,cn=kerberos_v4,cn=authzid
+> sasl-regexp
+> uid=(.*),cn=example.com,cn=kerberos_v4,cn=auth
> uid=$1,ou=person,dc=example,dc=com
An even more lenient rule could be written as
-> saslRegexp
-> uid=(.*),.*cn=authzid
+> sasl-regexp
+> uid=(.*),cn=.*,cn=auth
> uid=$1,ou=person,dc=example,dc=com
Be careful about setting the search pattern too leniently, however,
security holes. If there is only one authentication mechanism in
place at your site, and zero or one realms in use, you might be
able to map between authentication identities and LDAP DN's with
-a single {{EX:saslRegexp}} directive.
+a single {{EX:sasl-regexp}} directive.
+
+Don't forget to allow for the case where the realm is omitted as well
+as the case with an explicitly specified realm. This may well
+require a separate {{EX:sasl-regexp}} directive for each case, with the
+explicit-realm entry being listed first.
Some sites may have people's DN's spread to multiple areas of the
-LDAP tree, such as if there were an ou=accounting tree and an
-ou=engineering tree, with people interspersed between them. Or
+LDAP tree, such as if there were an {{EX:ou=accounting}} tree and an
+{{EX:ou=engineering}} tree, with people interspersed between them. Or
there may not be enough information in the authentication identity
to isolate the DN, such as if the above person's LDAP entry looked
like
In this case, the information in the authentication identity can
only be used to search for the user's DN, not derive it directly.
For both of these situations, and others, the replacement pattern
-in the {{EX:saslRegexp}} directives will need to produce an LDAP
+in the {{EX:sasl-regexp}} directives will need to produce an LDAP
URL, described in the next section.
H3: Performing searches for a person's DN
When there is not enough information in the authentication identity
-to derive a person's authentication DN directly, the {{EX:saslRegexp}}
+to derive a person's authentication DN directly, the {{EX:sasl-regexp}}
directives in the {{slapd.conf}}(5) file will need to produce an
LDAP URL. This URL will then be used to perform an internal search
of the LDAP database to find the person's authentication DN.
search: the name of the server <host>, the LDAP DN search base
<base>, the LDAP attributes to retrieve <attrs>, the search scope
<scope> which is one of the three options "base", "one", or "sub",
-and lastly an LDAP search filter <filter>. Since the search is for
-an LDAP DN on the local machine, the <host> portion is ignored. By
-the same token the <attrs> field is also ignored since only the DN
-is of concern. These two elements are left in the format of the
-URL to maintain the clarity of what information goes where in the
-string.
+and lastly an LDAP search filter <filter>. Since the search is for
+an LDAP DN within the current server, the <host> portion should be
+empty. The <attrs> field is also ignored since only the DN is of
+concern. These two elements are left in the format of the URL to
+maintain the clarity of what information goes where in the string.
Suppose that the person in the example from above did in fact have
an authentication username of "adamson" and that information was
-kept in the attribute "uid" in their LDAP entry. The {{EX:saslRegexp}}
+kept in the attribute "uid" in their LDAP entry. The {{EX:sasl-regexp}}
directive might be written as
-> saslRegexp
-> uid=(.*),cn=example.com,cn=kerberos_v4,cn=authzid
-> ldap://localhost/ou=person,dc=example,dc=com??sub?uid=$1
+> sasl-regexp
+> uid=(.*),cn=example.com,cn=kerberos_v4,cn=auth
+> ldap:///ou=person,dc=example,dc=com??sub?(uid=$1)
This will initiate an internal search of the LDAP database inside
the slapd server. If the search returns exactly one entry, it is
the authentication step alone can take uncomfortably long periods,
and users may assume the server is down.
-
-H2: SASL Authorization
-
-The SASL offers a feature known as {{authorization}}, which allows
-an authenticated user to request that they act on the behalf of
-another user. This step occurs after the user has obtained an
+A more complex site might have several realms in use, each mapping to
+a different sub-tree in the directory. These can be handled with
+statements of the form:
+
+> # Match Engineering realm
+> sasl-regexp
+> uid=(.*),cn=engineering.example.com,cn=digest-md5,cn=auth
+> ldap:///dc=eng,dc=example,dc=com??sub?(&(uid=$1)(objectClass=person))
+>
+> # Match Accounting realm
+> sasl-regexp
+> uid=(.*),cn=accounting.example.com,cn=digest-md5,cn=auth
+> ldap:///dc=accounting,dc=example,dc=com??sub?(&(uid=$1)(objectClass=person))
+>
+> # Default realm is customers.example.com
+> sasl-regexp
+> uid=(.*),cn=digest-md5,cn=auth
+> ldap:///dc=customers,dc=example,dc=com??sub?(&(uid=$1)(objectClass=person))
+
+Note that the explicitly-named realms are handled first, to avoid
+the realm name becoming part of the UID. Note also the limitation
+of matches to those entries with {{EX:(objectClass=person)}} to
+avoid matching other entries that happen to refer to the UID.
+
+See {{slapd.conf}}(5) for more detailed information.
+
+
+H2: SASL Proxy Authorization
+
+The SASL offers a feature known as {{proxy authorization}}, which
+allows an authenticated user to request that they act on the behalf
+of another user. This step occurs after the user has obtained an
authentication DN, and involves sending an authorization identity
to the server. The server will then make a decision on whether or
not to allow the authorization to occur. If it is allowed, the
cannot be made by SASL alone. The SASL library leaves it up to the
server to make the decision. The LDAP administrator sets the
guidelines of who can authorize to what identity by adding information
-into the LDAP database entries.
+into the LDAP database entries. By default, the authorization
+features are disabled, and must be explicitly configured by the
+LDAP administrator before use.
-H3: Uses of Authorization
+H3: Uses of Proxy Authorization
This sort of service is useful when one entity needs to act on the
behalf of many other users. For example, users may be directed to
of LDAP clients, knowledge which the web page provides in an easier
format.
-Authorization can also be used to limit access to an account that
-has greater access to the database. Such an account, perhaps even
-the root DN specified in {{slapd.conf}}(5), can have a strict list
-of people who can authorize to that DN. Changes to the LDAP database
-could then be only allowed by that DN, and in order to become that
-DN, users must first authenticate as one of the persons on the
-list. This allows for better auditing of who made changes to the
-LDAP database. If people were allowed to authenticate directly to
-the priviliged account, possibly through the {{EX:rootpw}}
+Proxy authorization can also be used to limit access to an account
+that has greater access to the database. Such an account, perhaps
+even the root DN specified in {{slapd.conf}}(5), can have a strict
+list of people who can authorize to that DN. Changes to the LDAP
+database could then be only allowed by that DN, and in order to
+become that DN, users must first authenticate as one of the persons
+on the list. This allows for better auditing of who made changes
+to the LDAP database. If people were allowed to authenticate
+directly to the priviliged account, possibly through the {{EX:rootpw}}
{{slapd.conf}}(5) directive or through a {{EX:userPassword}}
attribute, then auditing becomes more difficult.
-Note that after a successful authorization, the original authentication
-DN in the LDAP connection is overwritten by the new DN from the
-authorization request. If a service program is able to authenticate
-itself as its own authentication DN and then authorize to other
-DN's, and it is planning on switching to several different identities
-during one LDAP session, it will need to authenticate itself each
-time before authorizing to another DN. The slapd server does not
-keep record of the service program's ability to switch to other
-DN's. On authentication mechanisms like Kerberos this will not
-require multiple connections being made to the Kerberos server,
-since the user's TGT and "ldap" session key are valid for multiple
-uses for the several hours of the ticket lifetime.
+Note that after a successful proxy authorization, the original
+authentication DN of the LDAP connection is overwritten by the new
+DN from the authorization request. If a service program is able to
+authenticate itself as its own authentication DN and then authorize
+to other DN's, and it is planning on switching to several different
+identities during one LDAP session, it will need to authenticate
+itself each time before authorizing to another DN (or use a different
+proxy authorization mechanism). The slapd server does not keep
+record of the service program's ability to switch to other DN's.
+On authentication mechanisms like Kerberos this will not require
+multiple connections being made to the Kerberos server, since the
+user's TGT and "ldap" session key are valid for multiple uses for
+the several hours of the ticket lifetime.
-H3: Authorization Identities
+H3: SASL Authorization Identities
-The authorization identity is sent to the slapd server via the -X
-switch for {{ldapsearch}}(1) and other tools, or in the *authzid
-parameter to the {{lutil_sasl_defaults}}() call. The identity can
-be in one of two forms, either
+The SASL authorization identity is sent to the LDAP server via the
+{{EX:-X}} switch for {{ldapsearch}}(1) and other tools, or in the
+{{EX:*authzid}} parameter to the {{lutil_sasl_defaults}}() call.
+The identity can be in one of two forms, either
> u:<username>
by the same function that the authentication process used, producing
an {{authorization request DN}} of the form
-> uid=<username>,cn=<realm>,cn=authzid
+> uid=<username>,cn=<realm>,cn=<mechanism>,cn=auth
That authorization request DN is then run through the same
-{{EX:saslRegexp}} process to convert it into a legitimate authorization
+{{EX:sasl-regexp}} process to convert it into a legitimate authorization
DN from the database. If it cannot be converted due to a failed
search from an LDAP URL, the authorization request fails with
"inappropriate access". Otherwise, the DN string is now a legitimate
authorization DN ready to undergo approval.
If the authorization identity was provided in the second form, with
-a "dn:" prefix, the string after the prefix is already in authorization
-DN form, ready to undergo approval.
+a {{EX:"dn:"}} prefix, the string after the prefix is already in
+authorization DN form, ready to undergo approval.
-H3: Authorization rules
+H3: Proxy Authorization Rules
Once slapd has the authorization DN, the actual approval process
begins. There are two attributes that the LDAP administrator can
> saslAuthzTo
> saslAuthzFrom
-Both can be multivalued. The first is called a source rule, and it
-is placed into a person's authentication DN entry to tell what
-other authorization DN's the person is allowed to change to. The
-second form is called a destination rule, and it is placed into an
-authorization DN's entry to tell what authenticated DN a person
-must be coming from in order to switch to that authorization DN.
-The choice of which form to use is up to the administrator. Source
-rules are checked first in the person's authentication DN entry,
-and if none of the saslAuthzTo rules specify the authorization is
-permitted, the saslAuthzFrom rules in the authorization DN entry
-are then checked. If neither case specifies that the request be
-honored, the request is denied with an "inappropriate access"
-message. Since the default behaviour is to deny authorization
-requests, rules only specify that a request be allowed; there are
-no negative rules telling what authorizations to deny.
+Both can be multivalued. The {{EX:saslAuthzTo}} attribute is a
+source rule, and it is placed into the entry associated with the
+authentication DN to tell what authorization DNs the authenticated
+DN is allowed to assume. The second attribute is a destination
+rule, and it is placed into the entry associated with the requested
+authorization DN to tell which authenticated DNs may assume it.
+
+The choice of which authorization policy attribute to use is up to
+the administrator. Source rules are checked first in the person's
+authentication DN entry, and if none of the {{EX:saslAuthzTo}} rules
+specify the authorization is permitted, the {{EX:saslAuthzFrom}}
+rules in the authorization DN entry are then checked. If neither
+case specifies that the request be honored, the request is denied.
+Since the default behaviour is to deny authorization requests, rules
+only specify that a request be allowed; there are no negative rules
+telling what authorizations to deny.
The value(s) in the two attributes are of the same form as the
-output of the replacement pattern of a {{EX:saslRegexp}} directive:
-either a DN or an LDAP URL. For example, if a saslAuthzTo value is
-a DN, that DN is one the authenticated user can authorize to. On
-the other hand, if the saslAuthzTo value is an LDAP URL, the URL
-is used as an internal search of the LDAP database, and the
-authenticated user can become ANY DN returned by the search. If an
-LDAP entry looked like:
+output of the replacement pattern of a {{EX:sasl-regexp}} directive:
+either a DN or an LDAP URL. For example, if a {{EX:saslAuthzTo}}
+value is a DN, that DN is one the authenticated user can authorize
+to. On the other hand, if the {{EX:saslAuthzTo}} value is an LDAP
+URL, the URL is used as an internal search of the LDAP database,
+and the authenticated user can become ANY DN returned by the search.
+If an LDAP entry looked like:
> dn: cn=WebUpdate,dc=example,dc=com
-> saslAuthzTo: ldap://host/dc=example,dc=com??sub?objectclass=Person
+> saslAuthzTo: ldap:///dc=example,dc=com??sub?(objectclass=Person)
then any user who authenticated as cn=WebUpdate,dc=example,dc=com
could authorize to any other LDAP entry under the search base
"dc=example,dc=com" which has an objectClass of "Person".
-H4: Notes on Authorization rules
+H4: Notes on Proxy Authorization Rules
-An LDAP URL in a saslAuthzTo or saslAuthzFrom attribute will return
-a list of DN's, and that list must be linearly scanned. Searches
-which return a long list can cause the authorization process to
-take an uncomfortably long time. Also, searches should be performed
-on attributes that have been indexed by slapd.
+An LDAP URL in a {{EX:saslAuthzTo}} or {{EX:saslAuthzFrom}} attribute
+will return a set of DNs. Each DN returned will be checked.
+Searches which return a large set can cause the authorization
+process to take an uncomfortably long time. Also, searches should
+be performed on attributes that have been indexed by slapd.
-To help produce more sweeping rules for saslAuthzFrom and saslAuthzTo,
-the values of these attributes are allowed to be DN's with regular
-expression characters in them. This means a source rule like
+To help produce more sweeping rules for {{EX:saslAuthzFrom}} and
+{{EX:saslAuthzTo}}, the values of these attributes are allowed to
+be DNs with regular expression characters in them. This means a
+source rule like
> saslAuthzTo: uid=.*,dc=example,dc=com
would allow that authenticated user to authorize to any DN that
matches the regular expression pattern given. This regular expression
comparison can be evaluated much faster than an LDAP search for
-"uid=*".
+{{EX:(uid=*)}}.
Also note that the values in an authorization rule must be one of
the two forms: an LDAP URL or a DN (with or without regular expression
-characters). Anything that does not begin with "ldap://" is taken
-as a DN. It is not permissable to enter another authorization
-identity of the form "u:<username>" as an authorization rule.
-
-The decision of which type of rules to use, saslAuthzFrom or
-saslAuthzTo, will depend on the site's situation. For example, if
-the set of people who may become a given identity can easily be
-written as a search filter, then a single destination rule could
-be written. If the set of people is not easily defined by a search
-filter, and the set of people is small, it may be better to write
-a source rule in the entries of each of those people who should be
-allowed to perform the authorization.
-
+characters). Anything that does not begin with "{{EX:ldap://}}" is
+taken as a DN. It is not permissable to enter another authorization
+identity of the form "{{EX:u:<username>}}" as an authorization rule.
+
+
+H4: Policy Configuration
+
+The decision of which type of rules to use, {{EX:saslAuthzFrom}}
+or {{EX:saslAuthzTo}}, will depend on the site's situation. For
+example, if the set of people who may become a given identity can
+easily be written as a search filter, then a single destination
+rule could be written. If the set of people is not easily defined
+by a search filter, and the set of people is small, it may be better
+to write a source rule in the entries of each of those people who
+should be allowed to perform the proxy authorization.
+
+By default, processing of proxy authorization rules is disabled.
+The {{EX:sasl-authz-policy}} directive must be set in the
+{{slapd.conf}}(5) file to enable authorization. This directive can
+be set to {{EX:none}} for no rules (the default), {{EX:from}} for
+source rules, {{EX:to}} for destination rules, or {{EX:both}} for
+both source and destination rules.
+
+Destination rules are extremely powerful. If ordinary users have
+access to write the {{EX:saslAuthzTo}} attribute in their own entries, then
+they can write rules that would allow them to authorize as anyone else.
+As such, when using destination rules, the {{EX:saslAuthzTo}} attribute
+should be protected with an ACL that only allows privileged users
+to set its values.
projects / openldap / blobdiff