PAM_KRB5(8) BSD System Manager's Manual PAM_KRB5(8)
pam_krb5 -- Kerberos 5 PAM module
[service-name] function-class control-flag pam_krb5 [options]
The Kerberos 5 PAM module supports the authentication, account management and password management function classes. In terms of the
function-class parameter, these are ``auth'' , ``account'' and ``password'' respectively.
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 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
appropriately. The credentials cache should be destroyed by the user at logout with kdestroy(1).
The following options may be passed to this authentication module:
debug openpam_log(3) debugging information at PAM_LOG_DEBUG level.
use_first_pass If the authentication module is not the first in the stack, and a previous module obtained the user's password, that pass-
word 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.
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 designate the
decimal UID of the user; and '%p', to designate the current process ID; can be used in name.
default_principal Construct the principal from the authenticating user's username, rather than obtaining it from the AuthenticationAuthority
of the user's OpenDirectory record.
use_kcminit Don't verify password, instead store the password in kcm and return success in the pam chain. So when used in this mode,
the pam_krb5 module needs to be configured to be 'optional' and some other module 'required'.
Kerberos 5 Account Management Module
The Kerberos 5 account management component provides a function to perform 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
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 this 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 Ker-
beros password. If the new password fails, the password management module returns failure without prompting the user for a
try_first_pass This option is similar to the use_first_pass option, except that if the previously obtained old or new passwords fail, the
user is prompted for them.
KRB5CCNAME Location of the credentials cache.
/tmp/krb5cc_uid default credentials cache (uid is the decimal UID of the user).
$HOME/.k5login file containing Kerberos principals that are allowed access.
kdestroy(1), passwd(1), syslog(3), pam.conf(5), DirectoryService(8), pam(8)
Applications should not call pam_authenticate() more than once between calls to pam_start() and pam_end() when using the Kerberos 5 PAM mod-
January 15, 1999 BSD