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Diffstat (limited to 'doc/admin/host_config.rst')
| -rw-r--r-- | doc/admin/host_config.rst | 113 |
1 files changed, 113 insertions, 0 deletions
diff --git a/doc/admin/host_config.rst b/doc/admin/host_config.rst index 4bea576..6df2504 100644 --- a/doc/admin/host_config.rst +++ b/doc/admin/host_config.rst @@ -7,6 +7,119 @@ application servers, or KDCs, can be configured using you might want to make. +Default realm +------------- + +In the :ref:`libdefaults` section, the **default_realm** realm +relation sets the default Kerberos realm. For example:: + + [libdefaults] + default_realm = ATHENA.MIT.EDU + +The default realm affects Kerberos behavior in the following ways: + +* When a principal name is parsed from text, the default realm is used + if no ``@REALM`` component is specified. + +* The default realm affects login authorization as described below. + +* For programs which operate on a Kerberos database, the default realm + is used to determine which database to operate on, unless the **-r** + parameter is given to specify a realm. + +* A server program may use the default realm when looking up its key + in a :ref:`keytab file <keytab_file>`, if its realm is not + determined by :ref:`domain_realm` configuration or by the server + program itself. + +* If :ref:`kinit(1)` is passed the **-n** flag, it requests anonymous + tickets from the default realm. + +In some situations, these uses of the default realm might conflict. +For example, it might be desirable for principal name parsing to use +one realm by default, but for login authorization to use a second +realm. In this situation, the first realm can be configured as the +default realm, and **auth_to_local** relations can be used as +described below to use the second realm for login authorization. + + +.. _login_authorization: + +Login authorization +------------------- + +If a host runs a Kerberos-enabled login service such as OpenSSH with +GSSAPIAuthentication enabled, login authorization rules determine +whether a Kerberos principal is allowed to access a local account. + +By default, a Kerberos principal is allowed access to an account if +its realm matches the default realm and its name matches the account +name. (For historical reasons, access is also granted by default if +the name has two components and the second component matches the +default realm; for instance, ``alice/ATHENA.MIT.EDU@ATHENA.MIT.EDU`` +is granted access to the ``alice`` account if ``ATHENA.MIT.EDU`` is +the default realm.) + +The simplest way to control local access is using :ref:`.k5login(5)` +files. To use these, place a ``.k5login`` file in the home directory +of each account listing the principal names which should have login +access to that account. If it is not desirable to use ``.k5login`` +files located in account home directories, the **k5login_directory** +relation in the :ref:`libdefaults` section can specify a directory +containing one file per account uname. + +By default, if a ``.k5login`` file is present, it controls +authorization both positively and negatively--any principal name +contained in the file is granted access and any other principal name +is denied access, even if it would have had access if the ``.k5login`` +file didn't exist. The **k5login_authoritative** relation in the +:ref:`libdefaults` section can be set to false to make ``.k5login`` +files provide positive authorization only. + +The **auth_to_local** relation in the :ref:`realms` section for the +default realm can specify pattern-matching rules to control login +authorization. For example, the following configuration allows access +to principals from a different realm than the default realm:: + + [realms] + DEFAULT.REALM = { + # Allow access to principals from OTHER.REALM. + # + # [1:$1@$0] matches single-component principal names and creates + # a selection string containing the principal name and realm. + # + # (.*@OTHER\.REALM) matches against the selection string, so that + # only principals in OTHER.REALM are matched. + # + # s/@OTHER\.REALM$// removes the realm name, leaving behind the + # principal name as the acount name. + auth_to_local = RULE:[1:$1@$0](.*@OTHER\.REALM)s/@OTHER\.REALM$// + + # Also allow principals from the default realm. Omit this line + # to only allow access to principals in OTHER.REALM. + auth_to_local = DEFAULT + } + +The **auth_to_local_names** subsection of the :ref:`realms` section +for the default realm can specify explicit mappings from principal +names to local accounts. The key used in this subsection is the +principal name without realm, so it is only safe to use in a Kerberos +environment with a single realm or a tightly controlled set of realms. +An example use of **auth_to_local_names** might be:: + + [realms] + ATHENA.MIT.EDU = { + auth_to_local_names = { + # Careful, these match principals in any realm! + host/example.com = hostaccount + fred = localfred + } + } + +Local authorization behavior can also be modified using plugin +modules; see :ref:`hostrealm_plugin` for details. + + .. _plugin_config: Plugin module configuration |