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NetBSD 6.1.5 - man page for pam_krb5 (netbsd section 8)

PAM_KRB5(8)			   BSD System Manager's Manual			      PAM_KRB5(8)

NAME
     pam_krb5 -- Kerberos 5 PAM module

SYNOPSIS
     [service-name] module-type control-flag pam_krb5 [arguments]

DESCRIPTION
     The Kerberos 5 service module for PAM provides functionality for three PAM categories:
     authentication, account management, and password management.  It also provides null func-
     tions for session management.

   Kerberos 5 Authentication Module
     The Kerberos 5 authentication component provides functions to verify the identity of a user
     (pam_sm_authenticate()) and to set user specific credentials (pam_sm_setcred()).
     pam_sm_authenticate() converts the supplied username into a Kerberos principal, by appending
     the default local realm name.  It also supports usernames with explicit realm names.  If a
     realm name is supplied, then upon a successful return, it changes the username by mapping
     the principal name into a local username (calling krb5_aname_to_localname()).  This typi-
     cally just means the realm name is stripped.

     It prompts the user for a password and obtains a new Kerberos TGT for the principal.  The
     TGT is verified by obtaining a service ticket for the local host.

     When prompting for the current password, the authentication module will use the prompt
     ``Password for <principal>:''.

     The pam_sm_setcred() function stores the newly acquired credentials in a credentials cache,
     and sets the environment variable KRB5CCNAME appropriately.  The credentials cache should be
     destroyed by the user at logout with kdestroy(1).

     The following options may be passed to the authentication module:

     debug	     syslog(3) debugging information at LOG_DEBUG level.

     no_warn	     suppress warning messages to the user.  These messages include reasons why
		     the user's authentication attempt was declined.

     use_first_pass  If the authentication module is not the first in the stack, and a previous
		     module obtained the user's password, that password is used to authenticate
		     the user.	If this fails, the authentication module returns failure without
		     prompting the user for a password.  This option has no effect if the authen-
		     tication module is the first in the stack, or if no previous modules
		     obtained the user's password.

     try_first_pass  This option is similar to the use_first_pass option, except that if the pre-
		     viously obtained password fails, the user is prompted for another password.

     renewable=timeperiod
		     Obtain renewable Kerberos credentials for the user.  The renewable time can
		     be specified, or it defaults to one month.  Since spaces are not allowed in
		     the pam configuration time, underscores are used to form parseable times
		     (e.g., 1_month).

     forwardable     Obtain forwardable Kerberos credentials for the user.

     no_ccache	     Do not save the obtained credentials in a credentials cache.  This is a use-
		     ful option if the authentication module is used for services such as ftp or
		     pop, where the user would not be able to destroy them.  [This is not a rec-
		     ommendation to use the module for those services.]

     ccache=name     Use name as the credentials cache.  name must be in the form type:residual.
		     The special tokens '%u', to designate the decimal UID of the user; and '%p',
		     to designate the current process ID; can be used in name.

   Kerberos 5 Account Management Module
     The Kerberos 5 account management component provides a function to perform account manage-
     ment, pam_sm_acct_mgmt().	The function verifies that the authenticated principal is allowed
     to login to the local user account by calling krb5_kuserok() (which checks the user's
     .k5login file).

   Kerberos 5 Password Management Module
     The Kerberos 5 password management component provides a function to change passwords
     (pam_sm_chauthtok()).  The username supplied (the user running the passwd(1) command, or the
     username given as an argument) is mapped into a Kerberos principal name, using the same
     technique as in the authentication module.  Note that if a realm name was explicitly sup-
     plied during authentication, but not during a password change, the mapping done by the pass-
     word management module may not result in the same principal as was used for authentication.

     Unlike when changing a UNIX password, the password management module will allow any user to
     change any principal's password (if the user knows the principal's old password, of course).
     Also unlike UNIX, root is always prompted for the principal's old password.

     The password management module uses the same heuristics as kpasswd(1) to determine how to
     contact the Kerberos password server.

     The following options may be passed to the password management module:

     debug	     syslog(3) debugging information at LOG_DEBUG level.

     use_first_pass  If the password management module is not the first in the stack, and a pre-
		     vious module obtained the user's old password, that password is used to
		     authenticate the user.  If this fails, the password management module
		     returns failure without prompting the user for the old password.  If suc-
		     cessful, the new password entered to the previous module is also used as the
		     new Kerberos password.  If the new password fails, the password management
		     module returns failure without prompting the user for a new password.

     try_first_pass  This option is similar to the use_first_pass option, except that if the pre-
		     viously obtained old or new passwords fail, the user is prompted for them.

   Kerberos 5 Session Management Module
     The Kerberos 5 session management component provides functions to initiate
     (pam_sm_open_session()) and terminate (pam_sm_close_session()) sessions.  Since session man-
     agement is not defined under Kerberos 5, both of these functions simply return success.
     They are provided only because of the naming conventions for PAM modules.

ENVIRONMENT
     KRB5CCNAME  Location of the credentials cache.

FILES
     /tmp/krb5cc_uid  default credentials cache (uid is the decimal UID of the user).
     $HOME/.k5login   file containing Kerberos principals that are allowed access.

SEE ALSO
     kdestroy(1), passwd(1), syslog(3), pam.conf(5), pam(8)

NOTES
     Applications should not call pam_authenticate() more than once between calls to pam_start()
     and pam_end() when using the Kerberos 5 PAM module.

SECURITY CONSIDERATIONS
     The pam_krb5 module implements what is fundamentally a password authentication scheme.  It
     does not use a Kerberos 5 exchange between client and server, but rather authenticates the
     password provided by the client against the Kerberos KDC.	Therefore, care should be taken
     to only use this module over a secure session (secure TTY, encrypted session, etc.), other-
     wise the user's Kerberos 5 password could be compromised.

BSD					  March 10, 2007				      BSD


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