#include <u.h>#include <libc.h>#include <auth.h>#include "srv.h" enum{	CHALLEN	= 2 * AUTHLEN + 2 * NAMELEN,	RESPLEN	= 2 * AUTHLEN + NAMELEN + DESKEYLEN,	SULEN	= AUTHLEN + NAMELEN + DESKEYLEN,	MAXLEN	= 2*AUTHLEN + 2*NAMELEN + DESKEYLEN,}; char *srvauth(char *user){	char buf[MAXLEN], chal[AUTHLEN];	int fd; 	/*	 * get the kernel challenge and pass it to the terminal	 */	fd = open("#c/chal", OREAD);	if(fd < 0)		return "can't open challenge file";	if(read(fd, chal, AUTHLEN) != AUTHLEN){		close(fd);		return "can't read challenge";	}	close(fd);	if(write(1, chal, AUTHLEN) != AUTHLEN)		return "can't write challenge"; 	/*	 * forward the encrypted challenge from the terminal	 * to the auth server	 */	if(read(0, buf, CHALLEN) != CHALLEN)		return "can't read terminal challege";	strncpy(user, &buf[2*AUTHLEN+NAMELEN], NAMELEN);	fd = authdial("rexauth");	if(fd < 0)		return "can't call authentication server";	if(write(fd, buf, CHALLEN) != CHALLEN){		close(fd);		return "can't write terminal challenge";	}	if(read(fd, buf, RESPLEN) != RESPLEN){		close(fd);		return "failed to authenticate";	}	close(fd); 	if(write(1, buf, RESPLEN) != RESPLEN)		return "can't write to terminal";	if(read(0, buf, SULEN) != SULEN)		return "can't read from terminal";	netchown(user);	fd = open("#c/chal", OWRITE|OTRUNC);	if(fd < 0 || write(fd, buf, SULEN) != SULEN){		close(fd);		return "can't set user name";	}	close(fd);	write(1, "OK", 2);	return 0;}