sssd-krb5(5)
NAME
sssd-krb5 - SSSD Kerberos provider
DESCRIPTION
This manual page describes the configuration of the Kerberos 5
authentication backend for sssd(8). For a detailed syntax reference,
please refer to the "FILE FORMAT" section of the sssd.conf(5) manual
page.
The Kerberos 5 authentication backend contains auth and chpass
providers. It must be paired with an identity provider in order to
function properly (for example, id_provider = ldap). Some information
required by the Kerberos 5 authentication backend must be provided by
the identity provider, such as the user's Kerberos Principal Name
(UPN). The configuration of the identity provider should have an entry
to specify the UPN. Please refer to the man page for the applicable
identity provider for details on how to configure this.
This backend also provides access control based on the .k5login file in
the home directory of the user. See .k5login(5) for more details.
Please note that an empty .k5login file will deny all access to this
user. To activate this feature, use 'access_provider = krb5' in your
SSSD configuration.
In the case where the UPN is not available in the identity backend,
sssd will construct a UPN using the format username@krb5_realm.
CONFIGURATION OPTIONS
If the auth-module krb5 is used in an SSSD domain, the following
options must be used. See the sssd.conf(5) manual page, section "DOMAIN
SECTIONS", for details on the configuration of an SSSD domain.
krb5_server, krb5_backup_server (string)
Specifies the comma-separated list of IP addresses or hostnames of
the Kerberos servers to which SSSD should connect, in the order of
preference. For more information on failover and server redundancy,
see the "FAILOVER" section. An optional port number (preceded by a
colon) may be appended to the addresses or hostnames. If empty,
service discovery is enabled; for more information, refer to the
"SERVICE DISCOVERY" section.
When using service discovery for KDC or kpasswd servers, SSSD first
searches for DNS entries that specify _udp as the protocol and
falls back to _tcp if none are found.
This option was named "krb5_kdcip" in earlier releases of SSSD.
While the legacy name is recognized for the time being, users are
advised to migrate their config files to use "krb5_server" instead.
krb5_realm (string)
The name of the Kerberos realm. This option is required and must be
specified.
krb5_kpasswd, krb5_backup_kpasswd (string)
If the change password service is not running on the KDC,
alternative servers can be defined here. An optional port number
(preceded by a colon) may be appended to the addresses or
hostnames.
For more information on failover and server redundancy, see the
"FAILOVER" section. NOTE: Even if there are no more kpasswd servers
to try, the backend is not switched to operate offline if
authentication against the KDC is still possible.
Default: Use the KDC
krb5_ccachedir (string)
Directory to store credential caches. All the substitution
sequences of krb5_ccname_template can be used here, too, except %d
and %P. The directory is created as private and owned by the user,
with permissions set to 0700.
Default: /tmp
krb5_ccname_template (string)
Location of the user's credential cache. Three credential cache
types are currently supported: "FILE", "DIR" and
"KEYRING:persistent". The cache can be specified either as
TYPE:RESIDUAL, or as an absolute path, which implies the "FILE"
type. In the template, the following sequences are substituted:
%u
login name
%U
login UID
%p
principal name
%r
realm name
%h
home directory
%d
value of krb5_ccachedir
%P
the process ID of the SSSD client
%%
a literal '%'
If the template ends with 'XXXXXX' mkstemp(3) is used to create a
unique filename in a safe way.
When using KEYRING types, the only supported mechanism is
"KEYRING:persistent:%U", which uses the Linux kernel keyring to
store credentials on a per-UID basis. This is also the recommended
choice, as it is the most secure and predictable method.
The default value for the credential cache name is sourced from the
profile stored in the system wide krb5.conf configuration file in
the [libdefaults] section. The option name is default_ccache_name.
See krb5.conf(5)'s PARAMETER EXPANSION paragraph for additional
information on the expansion format defined by krb5.conf.
NOTE: Please be aware that libkrb5 ccache expansion template from
krb5.conf(5) uses different expansion sequences than SSSD.
Default: (from libkrb5)
krb5_auth_timeout (integer)
Timeout in seconds after an online authentication request or change
password request is aborted. If possible, the authentication
request is continued offline.
Default: 6
krb5_validate (boolean)
Verify with the help of krb5_keytab that the TGT obtained has not
been spoofed. The keytab is checked for entries sequentially, and
the first entry with a matching realm is used for validation. If no
entry matches the realm, the last entry in the keytab is used. This
process can be used to validate environments using cross-realm
trust by placing the appropriate keytab entry as the last entry or
the only entry in the keytab file.
Default: false
krb5_keytab (string)
The location of the keytab to use when validating credentials
obtained from KDCs.
Default: /etc/krb5.keytab
krb5_store_password_if_offline (boolean)
Store the password of the user if the provider is offline and use
it to request a TGT when the provider comes online again.
NOTE: this feature is only available on Linux. Passwords stored in
this way are kept in plaintext in the kernel keyring and are
potentially accessible by the root user (with difficulty).
Default: false
krb5_renewable_lifetime (string)
Request a renewable ticket with a total lifetime, given as an
integer immediately followed by a time unit:
s for seconds
m for minutes
h for hours
d for days.
If there is no unit given, s is assumed.
NOTE: It is not possible to mix units. To set the renewable
lifetime to one and a half hours, use '90m' instead of '1h30m'.
Default: not set, i.e. the TGT is not renewable
krb5_lifetime (string)
Request ticket with a lifetime, given as an integer immediately
followed by a time unit:
s for seconds
m for minutes
h for hours
d for days.
If there is no unit given s is assumed.
NOTE: It is not possible to mix units. To set the lifetime to one
and a half hours please use '90m' instead of '1h30m'.
Default: not set, i.e. the default ticket lifetime configured on
the KDC.
krb5_renew_interval (string)
The time in seconds between two checks if the TGT should be
renewed. TGTs are renewed if about half of their lifetime is
exceeded, given as an integer immediately followed by a time unit:
s for seconds
m for minutes
h for hours
d for days.
If there is no unit given, s is assumed.
NOTE: It is not possible to mix units. To set the renewable
lifetime to one and a half hours, use '90m' instead of '1h30m'.
If this option is not set or is 0 the automatic renewal is
disabled.
Default: not set
krb5_use_fast (string)
Enables flexible authentication secure tunneling (FAST) for
Kerberos pre-authentication. The following options are supported:
never use FAST. This is equivalent to not setting this option at
all.
try to use FAST. If the server does not support FAST, continue the
authentication without it.
demand to use FAST. The authentication fails if the server does not
require fast.
Default: not set, i.e. FAST is not used.
NOTE: a keytab is required to use FAST.
NOTE: SSSD supports FAST only with MIT Kerberos version 1.8 and
later. If SSSD is used with an older version of MIT Kerberos, using
this option is a configuration error.
krb5_fast_principal (string)
Specifies the server principal to use for FAST.
krb5_canonicalize (boolean)
Specifies if the host and user principal should be canonicalized.
This feature is available with MIT Kerberos 1.7 and later versions.
Default: false
krb5_use_kdcinfo (boolean)
Specifies if the SSSD should instruct the Kerberos libraries what
realm and which KDCs to use. This option is on by default, if you
disable it, you need to configure the Kerberos library using the
krb5.conf(5) configuration file.
See the sssd_krb5_locator_plugin(8) manual page for more
information on the locator plugin.
Default: true
krb5_use_enterprise_principal (boolean)
Specifies if the user principal should be treated as enterprise
principal. See section 5 of RFC 6806 for more details about
enterprise principals.
Default: false (AD provider: true)
krb5_map_user (string)
The list of mappings is given as a comma-separated list of pairs
"username:primary" where "username" is a UNIX user name and
"primary" is a user part of a kerberos principal. This mapping is
used when user is authenticating using "auth_provider = krb5".
example:
krb5_realm = REALM
krb5_map_user = joe:juser,dick:richard
"joe" and "dick" are UNIX user names and "juser" and "richard" are
primaries of kerberos principals. For user "joe" resp. "dick" SSSD
will try to kinit as "juser@REALM" resp. "richard@REALM".
Default: not set
FAILOVER
The failover feature allows back ends to automatically switch to a
different server if the current server fails.
Failover Syntax
The list of servers is given as a comma-separated list; any number of
spaces is allowed around the comma. The servers are listed in order of
preference. The list can contain any number of servers.
For each failover-enabled config option, two variants exist: primary
and backup. The idea is that servers in the primary list are preferred
and backup servers are only searched if no primary servers can be
reached. If a backup server is selected, a timeout of 31 seconds is
set. After this timeout SSSD will periodically try to reconnect to one
of the primary servers. If it succeeds, it will replace the current
active (backup) server.
The Failover Mechanism
The failover mechanism distinguishes between a machine and a service.
The back end first tries to resolve the hostname of a given machine; if
this resolution attempt fails, the machine is considered offline. No
further attempts are made to connect to this machine for any other
service. If the resolution attempt succeeds, the back end tries to
connect to a service on this machine. If the service connection attempt
fails, then only this particular service is considered offline and the
back end automatically switches over to the next service. The machine
is still considered online and might still be tried for another
service.
Further connection attempts are made to machines or services marked as
offline after a specified period of time; this is currently hard coded
to 30 seconds.
If there are no more machines to try, the back end as a whole switches
to offline mode, and then attempts to reconnect every 30 seconds.
SERVICE DISCOVERY
The service discovery feature allows back ends to automatically find
the appropriate servers to connect to using a special DNS query. This
feature is not supported for backup servers.
Configuration
If no servers are specified, the back end automatically uses service
discovery to try to find a server. Optionally, the user may choose to
use both fixed server addresses and service discovery by inserting a
special keyword, "_srv_", in the list of servers. The order of
preference is maintained. This feature is useful if, for example, the
user prefers to use service discovery whenever possible, and fall back
to a specific server when no servers can be discovered using DNS.
The domain name
Please refer to the "dns_discovery_domain" parameter in the
sssd.conf(5) manual page for more details.
The protocol
The queries usually specify _tcp as the protocol. Exceptions are
documented in respective option description.
See Also
For more information on the service discovery mechanism, refer to RFC
2782.
EXAMPLE
The following example assumes that SSSD is correctly configured and FOO
is one of the domains in the [sssd] section. This example shows only
configuration of Kerberos authentication; it does not include any
identity provider.
[domain/FOO]
auth_provider = krb5
krb5_server = 192.168.1.1
krb5_realm = EXAMPLE.COM
SEE ALSO
sssd(8), sssd.conf(5), sssd-ldap(5), sssd-krb5(5), sssd-simple(5),
sssd-ipa(5), sssd-ad(5), sssd-sudo(5), sss_cache(8), sss_debuglevel(8),
sss_groupadd(8), sss_groupdel(8), sss_groupshow(8), sss_groupmod(8),
sss_useradd(8), sss_userdel(8), sss_usermod(8), sss_obfuscate(8),
sss_seed(8), sssd_krb5_locator_plugin(8), sss_ssh_authorizedkeys(8),
sss_ssh_knownhostsproxy(8), sssd-ifp(5), pam_sss(8). sss_rpcidmapd(5)
AUTHORS
The SSSD upstream - http://fedorahosted.org/sssd
Free and Open Source Software