NOTE: the Sudo auth API is subject to change
Purpose: to provide a simple API for authentication methods that
encapsulates things nicely without turning into a maze
of #ifdef's
The sudo_auth struct looks like this:
typedef struct sudo_auth {
unsigned int flags; /* various flags, see below */
int status; /* status from verify routine */
char *name; /* name of the method in string form */
void *data; /* method-specific data pointer */
int (*init)(struct passwd *pw, sudo_auth *auth);
int (*setup)(struct passwd *pw, char **prompt, sudo_auth *auth);
int (*verify)(struct passwd *pw, const char *p, sudo_auth *auth, struct sudo_conv_callback *callback);
int (*approval)(struct passwd *pw, sudo_auth *auth);
int (*cleanup)(struct passwd *pw, sudo_auth *auth, bool force);
int (*begin_session)(struct passwd *pw, char **user_env[], struct sudo_auth *auth);
int (*end_session)(struct passwd *pw, struct sudo_auth *auth);
} sudo_auth;
The variables in the struct are as follows:
flags Bitwise binary flags, see below.
status Contains the return value from the last run of
the "verify" function. Starts out as AUTH_FAILURE.
name The name of the authentication method as a C string.
data A pointer to method-specific data. This is passed to
all the functions of an auth method and is usually
initialized in the "init" or "setup" routines.
Possible values of sudo_auth.flags:
FLAG_DISABLED Set if an "init" or "setup" function fails.
FLAG_STANDALONE If set, this indicates that the method must
be the only auth method configured, and that
it will prompt for the password itself.
FLAG_ONEANDONLY If set, this indicates that the method is the
only one in use. Can be used by auth functions
to determine whether to return a fatal or nonfatal
error.
FLAG_NONINTERACTIVE If set, this indicates that the user invoked
sudo with the -n option and no user interaction
is allowed.
The member functions can return the following values:
AUTH_SUCCESS Function succeeded. For a ``verify'' function
this means the user correctly authenticated.
AUTH_FAILURE Function failed. If this is an ``init'' or
``setup'' routine, the auth method will be
marked as !configured.
AUTH_ERROR A fatal error occurred. The routine should have
written an error message to stderr and optionally
sent mail to the administrator. When verify_user()
receives AUTH_ERROR from an auth function it stops
authenticating and returns an error.
AUTH_INTR An attempt to read the password read was interrupted.
Usually this means the user entered ^C at the
password prompt.
AUTH_NONINTERACTIVE Function failed because user interaction was
required but sudo was run in non-interactive
mode.
The functions in the struct are as follows:
int init(struct passwd *pw, sudo_auth *auth)
Function to do any one-time initialization for the auth
method. All of the "init" functions are run before anything
else.
int setup(struct passwd *pw, char **prompt, sudo_auth *auth)
Function to do method-specific setup. All the "setup"
routines are run before any of the "verify" routines. A
pointer to the prompt string may be used to add method-specific
info to the prompt.
int verify(struct passwd *pw, char *p, sudo_auth *auth, struct sudo_conv_callback *callback)
Function to do user verification for this auth method. For
standalone auth methods ``p'' is the prompt string. For
normal auth methods, ``p'' is the password the user entered.
The callback should be passed to auth_getpass() to allow sudoers
to unlock the ticket file when sudo is suspended.
Note that standalone auth methods are responsible for
rerading the password themselves.
int approval(struct passwd *pw, struct sudo_auth *auth)
Function to perform account management and approval *after*
the user has authenticated successfully. This function may
check for expired accounts, perform time of day restrictions, etc.
For PAM, this calls pam_acct_mgmt(). For BSD auth, it calls
auth_approval().
int cleanup(struct passwd *pw, sudo_auth *auth, bool force)
Function to do per-auth method cleanup. This is only run
at the end of the authentication process, after the user
has completely failed or succeeded to authenticate.
The ``auth->status'' variable contains the result of the
last authentication attempt which may be interesting.
If the force flag is set, cleanup should happen immediately.
int begin_session(struct passwd *pw, char **user_env[], struct sudo_auth *auth)
Function to begin a user session. This is used for session handling
in PAM and SIA.
int end_session(struct passwd *pw, struct sudo_auth *auth)
Function to end a user session. This is used for session handling
in PAM and SIA.
A note about standalone methods. Some authentication methods can't
coexist with any others. This may be because they encapsulate other
methods (pam, sia) or because they have a special way of interacting
with the user (securid).
Adding a new authentication method:
Each method should live in its own file. Add prototypes for the functions
in sudo_auth.h.
Add the method to the ``auth_switch'' in sudo_auth.c. Note that
standalone methods must go first. If ``fooauth'' is a normal auth
method, its entry would look like:
#ifdef HAVE_FOOAUTH
AUTH_ENTRY("foo", 0, foo_init, foo_setup, foo_verify,
foo_cleanup, foo_begin_session, foo_end_session)
#endif
If this is a standalone method, it would be:
#ifdef HAVE_FOOAUTH
AUTH_ENTRY("foo", FLAG_STANDALONE, foo_init, foo_setup, foo_verify,
foo_cleanup, foo_begin_session, foo_end_session)
#endif
If the method needs to run as the user, not root, add FLAG_USER to
the second argument in the AUTH_ENTRY line. If you don't have an
init/setup/cleanup/begin/end routine, just use a NULL for that
field.
