NAME
sssd-krb5 - SSSD Kerberos providerDESCRIPTION
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
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_keytab (string)
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 '%'
The location of the keytab to use when
validating credentials obtained from KDCs.
Default: System keytab, normally /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_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 or support for anonymous PKINIT 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_fast_use_anonymous_pkinit (boolean)
If set to true try to use anonymous PKINIT
instead of a keytab to get the required credential for FAST. The
krb5_fast_principal options is ignored in this case.
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_kdcinfo_lookahead (string)
When krb5_use_kdcinfo is set to true, you can
limit the amount of servers handed to sssd_krb5_locator_plugin(8). This
might be helpful when there are too many servers discovered using SRV record.
The krb5_kdcinfo_lookahead option contains two numbers separated by a colon. The
first number represents number of primary servers used and the second number
specifies the number of backup servers.
For example 10:0 means that up to 10 primary servers will be handed to
sssd_krb5_locator_plugin(8) but no backup servers.
Default: 3:1
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)
The IPA provider will set to option to 'true' if it detects that the server is
capable of handling enterprise principals and the option is not set explicitly
in the config file.
krb5_use_subdomain_realm (boolean)
Specifies to use subdomains realms for the
authentication of users from trusted domains. This option can be set to 'true'
if enterprise principals are used with upnSuffixes which are not known on the
parent domain KDCs. If the option is set to 'true' SSSD will try to send the
request directly to a KDC of the trusted domain the user is coming from.
Default: false
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:
“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
krb5_auth_timeout (integer)
krb5_realm = REALM krb5_map_user = joe:juser,dick:richard
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 (IPA and AD provider: true)
Please note that the ticket validation is the first step when checking the PAC
(see 'pac_check' in the sssd.conf(5) manual page for details). If
ticket validation is disabled the PAC checks will be skipped as well.
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_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
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.Failover time outs and tuning
Resolving a server to connect to can be as simple as running a single DNS query or can involve several steps, such as finding the correct site or trying out multiple host names in case some of the configured servers are not reachable. The more complex scenarios can take some time and SSSD needs to balance between providing enough time to finish the resolution process but on the other hand, not trying for too long before falling back to offline mode. If the SSSD debug logs show that the server resolution is timing out before a live server is contacted, you can consider changing the time outs. This section lists the available tunables. Please refer to their description in the sssd.conf(5), manual page. dns_resolver_server_timeoutTime in milliseconds that sets how long would
SSSD talk to a single DNS server before trying next one.
Default: 1000
dns_resolver_op_timeout
Time in seconds to tell how long would SSSD
try to resolve single DNS query (e.g. resolution of a hostname or an SRV
record) before trying the next hostname or discovery domain.
Default: 3
dns_resolver_timeout
How long would SSSD try to resolve a failover
service. This service resolution internally might include several steps, such
as resolving DNS SRV queries or locating the site.
Default: 6
For LDAP-based providers, the resolve operation is performed as part of an LDAP
connection operation. Therefore, also the “ldap_opt_timeout”
timeout should be set to a larger value than
“dns_resolver_timeout” which in turn should be set to a larger
value than “dns_resolver_op_timeout” which should be larger than
“dns_resolver_server_timeout”.
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-simple(5), sssd-ipa(5), sssd-ad(5), sssd-files(5), sssd-sudo(5), sssd-session-recording(5), sss_cache(8), sss_debuglevel(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) sssd-systemtap(5)AUTHORS
The SSSD upstream - https://github.com/SSSD/sssd/04/11/2023 | SSSD |