Auth Check

############################################################################
#                                                                          #
# auth_check()                      Version 1.0                            #
# Written by Craig A. Patchett      craig@patchett.com                     #
# Created 1/13/96                   Last Modified 11/16/96                 #
#                                                                          #
# Copyright 1996 Craig Patchett & Matthew Wright.  All Rights Reserved.    #
# This subroutine is part of The CGI/Perl Cookbook from John Wiley & Sons. #
# License to use this subroutine or install it on a server (in original or #
# modified form) is granted only to those who have purchased a copy of The #
# CGI/Perl Cookbook. (This notice must remain as part of the source code.) #
#                                                                          #
############################################################################


### Subroutine:    &auth_check()
###
### Function:      Checks to see if the caller of a program has entered a
###                valid user ID and password using the Authenticate program.
###                Will optionally call Authenticate if not.
###
### Usage:         &auth_check([$AUTHENTICATE]);
###
### Variables:     $AUTHENTICATE -- Optional non-zero value or string. If 
###                                 this argument is included and the visitor 
###                                 is not already authenticated, the 
###                                 subroutine will pass control over to 
###                                 Authenticate which will in turn pass 
###                                 control back to this URL after the 
###                                 visitor has been authenticated.
###                                 Example: 1
###
### Returns:       ($user_id, $last_visit) if visitor has been authenticated.
###                    $user_id is the visitor's user ID, $last_visit is the
###                    date of the visitor's last visit in time() format
###                (undefined, undefined) if a URL was not specified and the visitor
###                    has not been authenticated
###                Does not return if a URL was not specified and the visitor
###                    has not been authenticated (passes control to the
###                    Authenticate program specified by $AUTH_URL)
###
### Uses Global:   $AUTH_URL - See Authenticate
###                $AUTH_DIR - See Authenticate
###                $MAX_AGE  - See Authenticate
###
### Requires:      ipconvrt.pl
###                error.pl
###
### Files Created: None

sub auth_check {
	
	# Get argument (if any)
	
	local($AUTHENTICATE) = $_[0];
	
	# Set up other variables
	
	local($COOKIES, $auth_id, $auth_path, $auth_program, $valid, $user_id, $last_visit);
	local($date) = time;
	local($PROGRAM_URL) = "http://$ENV{'SERVER_NAME'}$ENV{'SCRIPT_NAME'}$ENV{'PATH_INFO'}";
	
	# Determine the authentication ID (if one exists)
	
	$auth_program = $AUTH_URL;
	$auth_program =~ s|http://[^/]+||;
	if ($ENV{'HTTP_COOKIE'} =~ /$auth_program=(\d+)/) { $auth_id = $1 }
	elsif (!$ENV{'HTTP_COOKIE'}) { 
		$auth_id = &ip_convert($ENV{'REMOTE_ADDR'}) 
	}
	
	# If an authentication ID exists, check to see if it's active
	
	$auth_path = "$AUTH_DIR$auth_id";
	if ($auth_id && (-f $auth_path) && (-r $auth_path) && 
	    (-M $auth_path < ($MAX_AGE / 1440))) {
	
		# File exists and is valid so set appropriate flag and update file
		
		open(AUTH, $auth_path) 
		  || &error("Could not open authentication file ($!).");
		$user_id = <AUTH>;
		close(AUTH);
		$last_visit = $^T - int((-M $auth_path) * 86400);

		open(AUTH, ">>$auth_path") 
		  || &error("Could not open authentication file ($!).");
		print AUTH "$PROGRAM_URL||$date\n";
		close(AUTH);		
		$valid = 1;
	}
	if (!$valid && $AUTHENTICATE) { 
	    print "Location: $AUTH_URL/$PROGRAM_URL\n\n"; 
	    exit(0);
	}
	else { return($user_id, $last_visit) }
}

1;