Two Factor Authentication With One Time Passwords with FreeRADIUS and LinOTP

Posted on July 15, 2012

The API

While the Enterprise Edition comes with a C module for the FreeRADIUS Server, the Community Edition, that is licensed under the AGPLv3 does not. Nevertheless, LinOTP provides very simple WEB APIs that makes it easy to talk to LinOTP in many different ways. There is also an API to do authentication, i.e. to ask the LinOTP server if a given one time password for a certain user is valid. This is the URL

https://yourServer/validate/check?user=….&pass=….

or

https://yourServer/validate/simplecheck?user=…&pass=…

You can take a look at the complete API here.

The FreeRADIUS

The simple LinOTP API and some nice module of the FreeRADIUS make it easy to hack a simple solution for OTP via RADIUS. You could use the module rlm_exec to execute an external program but I’d rather use the module rlm_perl and add my limited perl knowlege 😉

The documentation of the rlm_perl module can be found here. It has a simple example, that we need to adapt only in the function authenticate. This is the point, where we need to talk to the LinOTP server (with the above URL) and repond according the the LinOTP feedback.

Solution

Use this perl module (beta):
[sourcecode language=”perl”]
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
#
# Copyright 2002 The FreeRADIUS server project
# Copyright 2002 Boian Jordanov <bjordanov@orbitel.bg>
# Copyright 2011 linotp project <linotp@lsexperts.de>

#
# Based on the Example code for use with rlm_perl
#
#

=head1 NAME

freeradius_perl – Perl module for use with FreeRADIUS rlm_perl, to authenticate against
LinOTP http://www.linotp.org

=head1 SYNOPSIS

use with freeradius:

Configure rlm_perl to work with LinOTP:
in /etc/freeradius/users
set:
DEFAULT Auth-type := perl

in /etc/freeradius/modules/perl
point
perl {
module =
to this file

in /etc/freeradius/sites-enabled/<yoursite>
set
authenticate{
perl
[….]

=head1 DESCRIPTION

This module enables freeradius to authenticate using LinOTP.

TODO:
* checking of server certificate

=head2 Methods

* authenticate

=head1 AUTHOR

Cornelius Koelbel (cornelius.koelbel@lsexperts.de)

=head1 COPYRIGHT

Copyright 2011

This library is free software; you can redistribute it
under the GPLv2.

=head1 SEE ALSO

perl(1).

=cut

use strict;
use LWP 5.64;

# use …
# This is very important ! Without this script will not get the filled hashesh from main.
use vars qw(%RAD_REQUEST %RAD_REPLY %RAD_CHECK $URL);
use Data::Dumper;

$URL = "https://localhost/validate/simplecheck";

# This is hash wich hold original request from radius
#my %RAD_REQUEST;
# In this hash you add values that will be returned to NAS.
#my %RAD_REPLY;
#This is for check items
#my %RAD_CHECK;

#
# This the remapping of return values
#
use constant RLM_MODULE_REJECT=> 0;# /* immediately reject the request */
use constant RLM_MODULE_FAIL=> 1;# /* module failed, don’t reply */
use constant RLM_MODULE_OK=> 2;# /* the module is OK, continue */
use constant RLM_MODULE_HANDLED=> 3;# /* the module handled the request, so stop. */
use constant RLM_MODULE_INVALID=> 4;# /* the module considers the request invalid. */
use constant RLM_MODULE_USERLOCK=> 5;# /* reject the request (user is locked out) */
use constant RLM_MODULE_NOTFOUND=> 6;# /* user not found */
use constant RLM_MODULE_NOOP=> 7;# /* module succeeded without doing anything */
use constant RLM_MODULE_UPDATED=> 8;# /* OK (pairs modified) */
use constant RLM_MODULE_NUMCODES=> 9;# /* How many return codes there are */

# Function to handle authorize
sub authorize {
# For debugging purposes only
# &log_request_attributes;

# Here’s where your authorization code comes
# You can call another function from here:
&test_call;

return RLM_MODULE_OK;
}

# Function to handle authenticate
sub authenticate {
# For debugging purposes only
# &log_request_attributes;

my $ua = LWP::UserAgent->new();
my $req = HTTP::Request->new(GET => $URL . "?user=" .
$RAD_REQUEST{‘User-Name’} . "&pass=" .
$RAD_REQUEST{‘User-Password’} );
my $response = $ua->request( $req );

die "Error at $URL\n ", $response->status_line, "\n Aborting"
unless $response->is_success;

if($response->content =~ m/:\-\)/i) {
return RLM_MODULE_OK;
} else {
$RAD_REPLY{‘Reply-Message’} = "LinOTP server denied access!";
return RLM_MODULE_REJECT;
}
}

# Function to handle preacct
sub preacct {
# For debugging purposes only
# &log_request_attributes;

return RLM_MODULE_OK;
}

# Function to handle accounting
sub accounting {
# For debugging purposes only
# &log_request_attributes;

# You can call another subroutine from here
&test_call;

return RLM_MODULE_OK;
}

# Function to handle checksimul
sub checksimul {
# For debugging purposes only
# &log_request_attributes;

return RLM_MODULE_OK;
}

# Function to handle pre_proxy
sub pre_proxy {
# For debugging purposes only
# &log_request_attributes;

return RLM_MODULE_OK;
}

# Function to handle post_proxy
sub post_proxy {
# For debugging purposes only
# &log_request_attributes;

return RLM_MODULE_OK;
}

# Function to handle post_auth
sub post_auth {
# For debugging purposes only
# &log_request_attributes;

return RLM_MODULE_OK;
}

# Function to handle xlat
sub xlat {
# For debugging purposes only
# &log_request_attributes;

# Loads some external perl and evaluate it
my ($filename,$a,$b,$c,$d) = @_;
&radiusd::radlog(1, "From xlat $filename ");
&radiusd::radlog(1,"From xlat $a $b $c $d ");
local *FH;
open FH, $filename or die "open ‘$filename’ $!";
local($/) = undef;
my $sub = <FH>;
close FH;
my $eval = qq{ sub handler{ $sub;} };
eval $eval;
eval {main->handler;};
}

# Function to handle detach
sub detach {
# For debugging purposes only
# &log_request_attributes;

# Do some logging.
&radiusd::radlog(0,"rlm_perl::Detaching. Reloading. Done.");
}

#
# Some functions that can be called from other functions
#

sub test_call {
# Some code goes here
}

sub log_request_attributes {
# This shouldn’t be done in production environments!
# This is only meant for debugging!
for (keys %RAD_REQUEST) {
&radiusd::radlog(1, "RAD_REQUEST: $_ = $RAD_REQUEST{$_}");
}
}

1;
[/sourcecode]

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