LDAP

While many applications can support systems like Security Assertion Markup Language (SAML), or Open Authorization (OAuth), many do not. Lightweight Directory Access Protocol (LDAP) has been the "lingua franca" of authentication for many years, with almost every application in the world being able to search and bind to LDAP. As many organization still rely on LDAP, Kanidm can host a read-only LDAP interface.

WARNING The LDAP server in Kanidm is not RFC compliant. This is intentional, as Kanidm wants to cover the common use case, simple bind and search.

What is LDAP

LDAP is a protocol to read data from a directory of information. It is not a server, but a way to communicate to a server. There are many famous LDAP implementations such as Active Directory, 389 Directory Server, DSEE, FreeIPA, and many others. Because it is a standard, applications can use an LDAP client library to authenticate users to LDAP, given "one account" for many applications - an IDM just like Kanidm!

Data Mapping

Kanidm cannot be mapped 100% to LDAP's objects. This is because LDAP types are simple key-values on objects which are all UTF8 strings (or subsets thereof) based on validation (matching) rules. Kanidm internally implements complex data types such as tagging on SSH keys, or multi-value credentials. These can not be represented in LDAP.

Many of the structures in Kanidm do not correlate closely to LDAP. For example Kanidm only has a GID number, where LDAP's schemas define both a UID number and a GID number.

Entries in the database also have a specific name in LDAP, related to their path in the directory tree. Kanidm is a flat model, so we have to emulate some tree-like elements, and ignore others.

For this reason, when you search the LDAP interface, Kanidm will make some mapping decisions.

The domain_info object becomes the suffix root.
All other entries are direct subordinates of the domain_info for DN purposes.
Distinguished Names (DNs) are generated from the attributes naming attributes.
Bind DNs can be remapped and rewritten, and may not even be a DN during bind.
The Kanidm domain name is used to generate the base DN.
The '*' and '+' operators can not be used in conjuction with attribute lists in searches.

These decisions were made to make the path as simple and effective as possible, relying more on the Kanidm query and filter system than attempting to generate a tree-like representation of data. As almost all clients can use filters for entry selection we don't believe this is a limitation for the consuming applications.

Security

TLS

StartTLS is not supported due to security risks. LDAPS is the only secure method of communicating to any LDAP server. Kanidm, if configured with certificates, will use them for LDAPS (and will not listen on a plaintext LDAP port). If no certificates exist Kanidm will listen on a plaintext LDAP port, and you MUST TLS terminate in front of the Kanidm system to secure data and authentication.

Access Controls

LDAP only supports password authentication. As LDAP is used heavily in POSIX environments the LDAP bind for any DN will use its configured posix password.

As the POSIX password is not equivalent in strength to the primary credentials of Kanidm (which may be multi-factor authentication, MFA), the LDAP bind does not grant rights to elevated read permissions. All binds have the permissions of "Anonymous" even if the anonymous account is locked.

Server Configuration

To configure Kanidm to provide LDAP, add the argument to the server.toml configuration:

ldapbindaddress = "127.0.0.1:3636"

You should configure TLS certificates and keys as usual - LDAP will re-use the Web server TLS material.

Showing LDAP Entries and Attribute Maps

By default Kanidm is limited in what attributes are generated or remapped into LDAP entries. However, the server internally contains a map of extended attribute mappings for application specific requests that must be satisfied.

An example is that some applications expect and require a 'CN' value, even though Kanidm does not provide it. If the application is unable to be configured to accept "name" it may be necessary to use Kanidm's mapping feature. Currently these are compiled into the server, so you may need to open an issue with your requirements.

To show what attribute maps exists for an entry you can use the attribute search term '+'.

# To show Kanidm attributes
ldapsearch ... -x '(name=admin)' '*'
# To show all attribute maps
ldapsearch ... -x '(name=admin)' '+'

Attributes that are in the map can be requested explicitly, and this can be combined with requesting Kanidm native attributes.

ldapsearch ... -x '(name=admin)' cn objectClass displayname memberof

Example

Given a default install with domain "example.com" the configured LDAP DN will be "dc=example,dc=com". This can be queried with:

cargo run -- server -D kanidm.db -C ca.pem -c cert.pem -k key.pem -b 127.0.0.1:8443 -l 127.0.0.1:3636
> LDAPTLS_CACERT=ca.pem ldapsearch -H ldaps://127.0.0.1:3636 -b 'dc=example,dc=com' -x '(name=test1)'

# test1@example.com, example.com
dn: spn=test1@example.com,dc=example,dc=com
objectclass: account
objectclass: memberof
objectclass: object
objectclass: person
displayname: Test User
memberof: spn=group240@example.com,dc=example,dc=com
name: test1
spn: test1@example.com
entryuuid: 22a65b6c-80c8-4e1a-9b76-3f3afdff8400

It is recommended that client applications filter accounts that can login with '(class=account)' and groups with '(class=group)'. If possible, group membership is defined in RFC2307bis or Active Directory style. This means groups are determined from the "memberof" attribute which contains a DN to a group.

LDAP binds can use any unique identifier of the account. The following are all valid bind DNs for the object listed above (if it was a POSIX account, that is).

ldapwhoami ... -x -D 'name=test1'
ldapwhoami ... -x -D 'spn=test1@example.com'
ldapwhoami ... -x -D 'test1@example.com'
ldapwhoami ... -x -D 'test1'
ldapwhoami ... -x -D '22a65b6c-80c8-4e1a-9b76-3f3afdff8400'
ldapwhoami ... -x -D 'spn=test1@example.com,dc=example,dc=com'
ldapwhoami ... -x -D 'name=test1,dc=example,dc=com'

Most LDAP clients are very picky about TLS, and can be very hard to debug or display errors. For example these commands:

ldapsearch -H ldaps://127.0.0.1:3636 -b 'dc=example,dc=com' -x '(name=test1)'
ldapsearch -H ldap://127.0.0.1:3636 -b 'dc=example,dc=com' -x '(name=test1)'
ldapsearch -H ldap://127.0.0.1:3389 -b 'dc=example,dc=com' -x '(name=test1)'

All give the same error:

ldap_sasl_bind(SIMPLE): Can't contact LDAP server (-1)

This is despite the fact:

The first command is a certificate validation error.
The second is a missing LDAPS on a TLS port.
The third is an incorrect port.

To diagnose errors like this, you may need to add "-d 1" to your LDAP commands or client.

Kanidm Administration