% Login.c -- Prompting for username and password with ndialog
% Jessica L. Parsons <orc@pell.portland.or.us>
% Wed Jan 16 10:07:54 PST 2008

#Login.c

This code can be called by a login program to get a username and
password.  It expects that the world has been prepared by an
`init_dialog()` before it's called, and it leaves it up to the
caller to call `end_dialog()` when it wants to.

    /*
     * cc -c getuser.o getuser.c
     */
    #include <ndialog.h>
    #include <pwd.h>
    #include <sys/types.h>
    #include <unistd.h>

    #define ESIZE		20
    static char user[ESIZE];
    static char pass[ESIZE];
    static struct passwd *pw;
    static int retries;

    /*
     * pwcallback() is a local function that authenticates the user after they
     * enter a password.
     */
    static int
    pwcallback(void* obj, void* display)
    {
	char *ency;

	if ((pw = getpwnam(user)) != 0) {
	    if (pw->pw_passwd[0] == 0 && pass[0] == 0) {
		/* no password, so don't even check */
		return -1;
	    }
	    ency = crypt(pass, pw->pw_passwd);
	    memset(pass, 0, ESIZE);

	    if (strcmp(ency, pw->pw_passwd) == 0) {
		/* password matched; we can leave now */
		return -1;
	    }
	}
	/* complain bitterly and return */
	Error("login incorrect");
	return (--retries >= 0) ? 0 : -1;
    } /* pwcallback */


    /*
     * getuser() asks for a username and password.  If it's given a valid username
     * and password, it returns a pwent for that user, otherwise it spits up a
     * `login incorrect' error box and asks again, up to login_attempts times.
     * After that, it returns 0 and leaves the proper punishment up to the caller.
     */
    struct passwd *
    getuser(int login_attempts)
    {
	int rc;
	void *u_obj, *p_obj, *cancel, *chain;

	/* allocate the display fields */
	u_obj = newString(  0,0, ESIZE, ESIZE, user, 0, "Username", 0, 0);
	p_obj = newPWString(0,3, ESIZE, ESIZE, pass, 0, "Password", pwcallback, 0);
	cancel= newCancelButton(0, "Forget it", 0, 0);
	retries = login_attempts;

	/* build them into a ObjChain */
	chain = ObjChain(ObjChain(u_obj, p_obj), cancel);

	/* get the user input and clean up */
	rc = MENU(chain, -1, -1, 0, "Enter your username and password", 0);
	deleteObjChain(chain);

	/* and return the user info if there is any */
	return (rc == MENU_OK) ? pw : 0;
    } /* getuser */