PAM_KRB5(8)             NetBSD 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 manage-
     ment.  It also provides null functions 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 cre-
     dentials (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 typically 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 appropri-
     ately.  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 pass-
                     word, 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 authentication 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 previously 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 configu-
                     ration 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 useful 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
                     recommendation 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 desig-
                     nate 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 per-
     form account management, 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 supplied
     during authentication, but not during a password change, the mapping done
     by the password 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 previous 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 successful, 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 previously obtained old or new pass-
                     words fail, the user is prompted for them.

   Kerberos 5 Session Management Module
     The Kerberos 5 session management component provides functions to initi-
     ate (pam_sm_open_session()) and terminate (pam_sm_close_session()) ses-
     sions.  Since session management 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 authenti-
     cation 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.),
     otherwise the user's Kerberos 5 password could be compromised.

NetBSD 5.1                      March 10, 2007                      NetBSD 5.1

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