1SSSD-KRB5(5)             File Formats and Conventions             SSSD-KRB5(5)
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NAME

6       sssd-krb5 - SSSD Kerberos provider
7

DESCRIPTION

9       This manual page describes the configuration of the Kerberos 5
10       authentication backend for sssd(8). For a detailed syntax reference,
11       please refer to the “FILE FORMAT” section of the sssd.conf(5) manual
12       page.
13
14       The Kerberos 5 authentication backend contains auth and chpass
15       providers. It must be paired with an identity provider in order to
16       function properly (for example, id_provider = ldap). Some information
17       required by the Kerberos 5 authentication backend must be provided by
18       the identity provider, such as the user's Kerberos Principal Name
19       (UPN). The configuration of the identity provider should have an entry
20       to specify the UPN. Please refer to the man page for the applicable
21       identity provider for details on how to configure this.
22
23       This backend also provides access control based on the .k5login file in
24       the home directory of the user. See k5login(5) for more details. Please
25       note that an empty .k5login file will deny all access to this user. To
26       activate this feature, use 'access_provider = krb5' in your SSSD
27       configuration.
28
29       In the case where the UPN is not available in the identity backend,
30       sssd will construct a UPN using the format username@krb5_realm.
31

CONFIGURATION OPTIONS

33       If the auth-module krb5 is used in an SSSD domain, the following
34       options must be used. See the sssd.conf(5) manual page, section “DOMAIN
35       SECTIONS”, for details on the configuration of an SSSD domain.
36
37       krb5_server, krb5_backup_server (string)
38           Specifies the comma-separated list of IP addresses or hostnames of
39           the Kerberos servers to which SSSD should connect, in the order of
40           preference. For more information on failover and server redundancy,
41           see the “FAILOVER” section. An optional port number (preceded by a
42           colon) may be appended to the addresses or hostnames. If empty,
43           service discovery is enabled; for more information, refer to the
44           “SERVICE DISCOVERY” section.
45
46           When using service discovery for KDC or kpasswd servers, SSSD first
47           searches for DNS entries that specify _udp as the protocol and
48           falls back to _tcp if none are found.
49
50           This option was named “krb5_kdcip” in earlier releases of SSSD.
51           While the legacy name is recognized for the time being, users are
52           advised to migrate their config files to use “krb5_server” instead.
53
54       krb5_realm (string)
55           The name of the Kerberos realm. This option is required and must be
56           specified.
57
58       krb5_kpasswd, krb5_backup_kpasswd (string)
59           If the change password service is not running on the KDC,
60           alternative servers can be defined here. An optional port number
61           (preceded by a colon) may be appended to the addresses or
62           hostnames.
63
64           For more information on failover and server redundancy, see the
65           “FAILOVER” section. NOTE: Even if there are no more kpasswd servers
66           to try, the backend is not switched to operate offline if
67           authentication against the KDC is still possible.
68
69           Default: Use the KDC
70
71       krb5_ccachedir (string)
72           Directory to store credential caches. All the substitution
73           sequences of krb5_ccname_template can be used here, too, except %d
74           and %P. The directory is created as private and owned by the user,
75           with permissions set to 0700.
76
77           Default: /tmp
78
79       krb5_ccname_template (string)
80           Location of the user's credential cache. Three credential cache
81           types are currently supported: “FILE”, “DIR” and
82           “KEYRING:persistent”. The cache can be specified either as
83           TYPE:RESIDUAL, or as an absolute path, which implies the “FILE”
84           type. In the template, the following sequences are substituted:
85
86           %u
87               login name
88
89           %U
90               login UID
91
92           %p
93               principal name
94
95           %r
96               realm name
97
98           %h
99               home directory
100
101           %d
102               value of krb5_ccachedir
103
104           %P
105               the process ID of the SSSD client
106
107           %%
108               a literal '%'
109
110           If the template ends with 'XXXXXX' mkstemp(3) is used to create a
111           unique filename in a safe way.
112
113           When using KEYRING types, the only supported mechanism is
114           “KEYRING:persistent:%U”, which uses the Linux kernel keyring to
115           store credentials on a per-UID basis. This is also the recommended
116           choice, as it is the most secure and predictable method.
117
118           The default value for the credential cache name is sourced from the
119           profile stored in the system wide krb5.conf configuration file in
120           the [libdefaults] section. The option name is default_ccache_name.
121           See krb5.conf(5)'s PARAMETER EXPANSION paragraph for additional
122           information on the expansion format defined by krb5.conf.
123
124           NOTE: Please be aware that libkrb5 ccache expansion template from
125           krb5.conf(5) uses different expansion sequences than SSSD.
126
127           Default: (from libkrb5)
128
129       krb5_keytab (string)
130           The location of the keytab to use when validating credentials
131           obtained from KDCs.
132
133           Default: System keytab, normally /etc/krb5.keytab
134
135       krb5_store_password_if_offline (boolean)
136           Store the password of the user if the provider is offline and use
137           it to request a TGT when the provider comes online again.
138
139           NOTE: this feature is only available on Linux. Passwords stored in
140           this way are kept in plaintext in the kernel keyring and are
141           potentially accessible by the root user (with difficulty).
142
143           Default: false
144
145       krb5_use_fast (string)
146           Enables flexible authentication secure tunneling (FAST) for
147           Kerberos pre-authentication. The following options are supported:
148
149           never use FAST. This is equivalent to not setting this option at
150           all.
151
152           try to use FAST. If the server does not support FAST, continue the
153           authentication without it.
154
155           demand to use FAST. The authentication fails if the server does not
156           require fast.
157
158           Default: not set, i.e. FAST is not used.
159
160           NOTE: a keytab is required to use FAST.
161
162           NOTE: SSSD supports FAST only with MIT Kerberos version 1.8 and
163           later. If SSSD is used with an older version of MIT Kerberos, using
164           this option is a configuration error.
165
166       krb5_fast_principal (string)
167           Specifies the server principal to use for FAST.
168
169       krb5_use_kdcinfo (boolean)
170           Specifies if the SSSD should instruct the Kerberos libraries what
171           realm and which KDCs to use. This option is on by default, if you
172           disable it, you need to configure the Kerberos library using the
173           krb5.conf(5) configuration file.
174
175           See the sssd_krb5_locator_plugin(8) manual page for more
176           information on the locator plugin.
177
178           Default: true
179
180       krb5_kdcinfo_lookahead (string)
181           When krb5_use_kdcinfo is set to true, you can limit the amount of
182           servers handed to sssd_krb5_locator_plugin(8). This might be
183           helpful when there are too many servers discovered using SRV
184           record.
185
186           The krb5_kdcinfo_lookahead option contains two numbers separated by
187           a colon. The first number represents number of primary servers used
188           and the second number specifies the number of backup servers.
189
190           For example 10:0 means that up to 10 primary servers will be handed
191           to sssd_krb5_locator_plugin(8) but no backup servers.
192
193           Default: 3:1
194
195       krb5_use_enterprise_principal (boolean)
196           Specifies if the user principal should be treated as enterprise
197           principal. See section 5 of RFC 6806 for more details about
198           enterprise principals.
199
200           Default: false (AD provider: true)
201
202           The IPA provider will set to option to 'true' if it detects that
203           the server is capable of handling enterprise principals and the
204           option is not set explicitly in the config file.
205
206       krb5_use_subdomain_realm (boolean)
207           Specifies to use subdomains realms for the authentication of users
208           from trusted domains. This option can be set to 'true' if
209           enterprise principals are used with upnSuffixes which are not known
210           on the parent domain KDCs. If the option is set to 'true' SSSD will
211           try to send the request directly to a KDC of the trusted domain the
212           user is coming from.
213
214           Default: false
215
216       krb5_map_user (string)
217           The list of mappings is given as a comma-separated list of pairs
218           “username:primary” where “username” is a UNIX user name and
219           “primary” is a user part of a kerberos principal. This mapping is
220           used when user is authenticating using “auth_provider = krb5”.
221
222           example:
223
224               krb5_realm = REALM
225               krb5_map_user = joe:juser,dick:richard
226
227           “joe” and “dick” are UNIX user names and “juser” and “richard” are
228           primaries of kerberos principals. For user “joe” resp.  “dick” SSSD
229           will try to kinit as “juser@REALM” resp.  “richard@REALM”.
230
231           Default: not set
232
233       krb5_auth_timeout (integer)
234           Timeout in seconds after an online authentication request or change
235           password request is aborted. If possible, the authentication
236           request is continued offline.
237
238           Default: 6
239
240       krb5_validate (boolean)
241           Verify with the help of krb5_keytab that the TGT obtained has not
242           been spoofed. The keytab is checked for entries sequentially, and
243           the first entry with a matching realm is used for validation. If no
244           entry matches the realm, the last entry in the keytab is used. This
245           process can be used to validate environments using cross-realm
246           trust by placing the appropriate keytab entry as the last entry or
247           the only entry in the keytab file.
248
249           Default: false
250
251       krb5_renewable_lifetime (string)
252           Request a renewable ticket with a total lifetime, given as an
253           integer immediately followed by a time unit:
254
255           s for seconds
256
257           m for minutes
258
259           h for hours
260
261           d for days.
262
263           If there is no unit given, s is assumed.
264
265           NOTE: It is not possible to mix units. To set the renewable
266           lifetime to one and a half hours, use '90m' instead of '1h30m'.
267
268           Default: not set, i.e. the TGT is not renewable
269
270       krb5_lifetime (string)
271           Request ticket with a lifetime, given as an integer immediately
272           followed by a time unit:
273
274           s for seconds
275
276           m for minutes
277
278           h for hours
279
280           d for days.
281
282           If there is no unit given s is assumed.
283
284           NOTE: It is not possible to mix units. To set the lifetime to one
285           and a half hours please use '90m' instead of '1h30m'.
286
287           Default: not set, i.e. the default ticket lifetime configured on
288           the KDC.
289
290       krb5_renew_interval (string)
291           The time in seconds between two checks if the TGT should be
292           renewed. TGTs are renewed if about half of their lifetime is
293           exceeded, given as an integer immediately followed by a time unit:
294
295           s for seconds
296
297           m for minutes
298
299           h for hours
300
301           d for days.
302
303           If there is no unit given, s is assumed.
304
305           NOTE: It is not possible to mix units. To set the renewable
306           lifetime to one and a half hours, use '90m' instead of '1h30m'.
307
308           If this option is not set or is 0 the automatic renewal is
309           disabled.
310
311           Default: not set
312
313       krb5_canonicalize (boolean)
314           Specifies if the host and user principal should be canonicalized.
315           This feature is available with MIT Kerberos 1.7 and later versions.
316
317           Default: false
318

FAILOVER

320       The failover feature allows back ends to automatically switch to a
321       different server if the current server fails.
322
323   Failover Syntax
324       The list of servers is given as a comma-separated list; any number of
325       spaces is allowed around the comma. The servers are listed in order of
326       preference. The list can contain any number of servers.
327
328       For each failover-enabled config option, two variants exist: primary
329       and backup. The idea is that servers in the primary list are preferred
330       and backup servers are only searched if no primary servers can be
331       reached. If a backup server is selected, a timeout of 31 seconds is
332       set. After this timeout SSSD will periodically try to reconnect to one
333       of the primary servers. If it succeeds, it will replace the current
334       active (backup) server.
335
336   The Failover Mechanism
337       The failover mechanism distinguishes between a machine and a service.
338       The back end first tries to resolve the hostname of a given machine; if
339       this resolution attempt fails, the machine is considered offline. No
340       further attempts are made to connect to this machine for any other
341       service. If the resolution attempt succeeds, the back end tries to
342       connect to a service on this machine. If the service connection attempt
343       fails, then only this particular service is considered offline and the
344       back end automatically switches over to the next service. The machine
345       is still considered online and might still be tried for another
346       service.
347
348       Further connection attempts are made to machines or services marked as
349       offline after a specified period of time; this is currently hard coded
350       to 30 seconds.
351
352       If there are no more machines to try, the back end as a whole switches
353       to offline mode, and then attempts to reconnect every 30 seconds.
354
355   Failover time outs and tuning
356       Resolving a server to connect to can be as simple as running a single
357       DNS query or can involve several steps, such as finding the correct
358       site or trying out multiple host names in case some of the configured
359       servers are not reachable. The more complex scenarios can take some
360       time and SSSD needs to balance between providing enough time to finish
361       the resolution process but on the other hand, not trying for too long
362       before falling back to offline mode. If the SSSD debug logs show that
363       the server resolution is timing out before a live server is contacted,
364       you can consider changing the time outs.
365
366       This section lists the available tunables. Please refer to their
367       description in the sssd.conf(5), manual page.
368
369       dns_resolver_server_timeout
370           Time in milliseconds that sets how long would SSSD talk to a single
371           DNS server before trying next one.
372
373           Default: 1000
374
375       dns_resolver_op_timeout
376           Time in seconds to tell how long would SSSD try to resolve single
377           DNS query (e.g. resolution of a hostname or an SRV record) before
378           trying the next hostname or discovery domain.
379
380           Default: 3
381
382       dns_resolver_timeout
383           How long would SSSD try to resolve a failover service. This service
384           resolution internally might include several steps, such as
385           resolving DNS SRV queries or locating the site.
386
387           Default: 6
388
389       For LDAP-based providers, the resolve operation is performed as part of
390       an LDAP connection operation. Therefore, also the “ldap_opt_timeout”
391       timeout should be set to a larger value than “dns_resolver_timeout”
392       which in turn should be set to a larger value than
393       “dns_resolver_op_timeout” which should be larger than
394       “dns_resolver_server_timeout”.
395

SERVICE DISCOVERY

397       The service discovery feature allows back ends to automatically find
398       the appropriate servers to connect to using a special DNS query. This
399       feature is not supported for backup servers.
400
401   Configuration
402       If no servers are specified, the back end automatically uses service
403       discovery to try to find a server. Optionally, the user may choose to
404       use both fixed server addresses and service discovery by inserting a
405       special keyword, “_srv_”, in the list of servers. The order of
406       preference is maintained. This feature is useful if, for example, the
407       user prefers to use service discovery whenever possible, and fall back
408       to a specific server when no servers can be discovered using DNS.
409
410   The domain name
411       Please refer to the “dns_discovery_domain” parameter in the
412       sssd.conf(5) manual page for more details.
413
414   The protocol
415       The queries usually specify _tcp as the protocol. Exceptions are
416       documented in respective option description.
417
418   See Also
419       For more information on the service discovery mechanism, refer to RFC
420       2782.
421

EXAMPLE

423       The following example assumes that SSSD is correctly configured and FOO
424       is one of the domains in the [sssd] section. This example shows only
425       configuration of Kerberos authentication; it does not include any
426       identity provider.
427
428           [domain/FOO]
429           auth_provider = krb5
430           krb5_server = 192.168.1.1
431           krb5_realm = EXAMPLE.COM
432
433

SEE ALSO

435       sssd(8), sssd.conf(5), sssd-ldap(5), sssd-krb5(5), sssd-simple(5),
436       sssd-ipa(5), sssd-ad(5), sssd-files(5), sssd-sudo(5), sssd-session-
437       recording(5), sss_cache(8), sss_debuglevel(8), sss_obfuscate(8),
438       sss_seed(8), sssd_krb5_locator_plugin(8), sss_ssh_authorizedkeys(8),
439       sss_ssh_knownhostsproxy(8), sssd-ifp(5), pam_sss(8).  sss_rpcidmapd(5)
440       sssd-systemtap(5)
441

AUTHORS

443       The SSSD upstream - https://github.com/SSSD/sssd/
444
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446
447SSSD                              11/08/2021                      SSSD-KRB5(5)
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