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 {
    short flags;                /* various flags, see below */
    short status;               /* status from verify routine */
    char *name;			/* name of the method in string form */
    void *data;                 /* method-specific data pointer */

    int (*init) __P((struct passwd *pw, char **prompt, sudo_auth *auth));
    int (*setup) __P((struct passwd *pw, char **prompt, sudo_auth *auth));
    int (*verify) __P((struct passwd *pw, char *p, sudo_auth *auth));
    int (*cleanup) __P((struct passwd *pw, 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_USER		Whether or not the auth functions should run with
			the euid of the invoking user instead of 0.

    FLAG_CONFIGURED	If set then the auth method is assumed to have been
			configured successfully.  All auth methods start out
			with this set.  If an "init" or "setup" function
			fails, this bit is cleared.

    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.

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_FATAL		A fatal error occurred.  The routine should have
			written an error message to stderr and optionally
			sent mail to the administrator.  (If log_error()
			is called to do this, the NO_EXIT flag must be used.)
			When verify_user() gets AUTH_FATAL from an auth
			function it does an exit(1).

The functions in the struct are as follows:

    int init(struct passwd *pw, char **prompt, sudo_auth *auth)
        Function to do any one-time initialization for the auth
        method.  All of the "init" functions are run before anything
        else.  A pointer to the prompt string may be used to add
        method-specific info to the prompt.

    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)
        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.
        Note that standalone auth methods are responsible for
        rerading the password themselves.

    int cleanup(struct passwd *pw, sudo_auth *auth)
        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.

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.

If this is a standalone method, add it to the standalone #if cascade
in sudo_auth.h.  For instance, for a method, ``fooauth'', add:

#elif defined(HAVE_FOOAUTH)
#  define AUTH_STANDALONE \
        AUTH_ENTRY(0, "foo", \
	    foo_init, foo_setup, foo_verify, foo_cleanup)

If the method needs to run as the user, not root, replace the first
parameter to AUTH_ENTRY (0) with FLAG_USER.  If you don't have a
init/setup/cleanup routine, just use a NULL for that field.

For a normal authentication method, add it to the ``auth_switch'' in
sudo_auth.c.  If ``fooauth'' is a normal auth method, its entry
would look like:

#  ifdef HAVE_FOOAUTH
    AUTH_ENTRY(0, "foo", foo_init, foo_setup, foo_verify, foo_cleanup)
#  endif

Again, if the method doesn't need to run as root, replace the 0 with
FLAG_USER.  Likewise, if you don't have a init/setup/cleanup routine,
just use a NULL for that field.

NOTE:  You should not make a method both ``standalone'' and
       ``normal''.  Just use the --without-passwd configure argument
       to disable passwd/shadow file checking and then have your
       auth routines check the FLAG_ONEANDONLY flag to see if
       they are running standalone and act accordingly.