NAME

Google::SAML::Response - Generate signed XML documents as SAML responses for Google's SSO implementation

VERSION

You are currently reading the documentation for version 0.14

DESCRIPTION

Google::SAML::Response can be used to generate a signed XML document that is needed for logging your users into Google using SSO.

You have some sort of web application that can identify and authenticate users. You want users to be able to use some sort of Google service such as Google mail.

When using SSO with your Google partner account, your users will send a request to a Google URL. If the user isn't already logged in to Google, Google will redirect him to a URL that you can define. Behind this URL, you need to have a script that authenticates users in your original framework and generates a SAML response for Google that you send back to the user whose browser will then submit it back to Google. If everything works, users will then be logged into their Google account and they don't even have to know their usernames or passwords.

SYNOPSIS

 use Google::SAML::Response;
 use CGI;

 # get SAMLRequest parameter:
 my $req = CGI->new->param('SAMLRequest');

 # authenticate user
 ...

 # find our user's login for Google
 ...

 # Generate SAML response
 my $saml = Google::SAML::Response->new( { 
                            key     => $key, 
                            login   => $login, 
                            request => $req 
            } );
 my $xml  = $saml->get_response_xml;

 # Alternatively, send a HTML page to the client that will redirect
 # her to Google. You have to extract the RelayState param from the cgi
 # environment first.

 print $saml->get_google_form( $relayState );

PREREQUISITES

You will need the following modules installed:

Crypt::OpenSSL::RSA
Crypt::OpenSSL::Bignum
XML::Canonical or XML::CanonicalizeXML
Digest::SHA
Date::Format
Google::SAML::Request

RESOURCES

XML-Signature Syntax and Processing: <http://www.w3.org/TR/xmldsig-core/>
Google-Documentation on SSO and SAML: <https://developers.google.com/google-apps/sso/saml_reference_implementation>
XML Security Library: <http://www.aleksey.com/xmlsec/>

METHODS

new

Creates a new object and needs to have all parameters needed to generate the signed xml later on. Parameters are passed in as a hash-reference.

Required parameters

request
The SAML request, base64-encoded and all, just as retrieved from the GET request your user contacted you with (make sure that it's not url-encoded, though)
key
The path to your private key that will be used to sign the response. Currently, only RSA and DSA keys without pass phrases are supported. NOTE: To handle DSA keys, the module Crypt::OpenSSL::DSA needs to be installed. However, it is not listed as a requirement in the Makefile for Google::SAML::Response, so make sure it really is installed before using DSA keys.
login
Your user's login name with Google

Optional parameters

ttl
Time to live: Number of seconds your response should be valid. Default is two minutes.
canonicalizer
The name of the module that will be used to canonicalize parts of our xml. Currently, XML::Canonical and XML::CanonicalizeXML are supported. XML::CanonicalizeXML is the default.

get_response_xml

Generate the signed response xml and return it as a string

The method does what the w3c tells us to do (<http://www.w3.org/TR/xmldsig-core/#sec-CoreGeneration>):

3.1.1 Reference Generation

For each data object being signed:

1. Apply the Transforms, as determined by the application, to the data object.

2. Calculate the digest value over the resulting data object.

3. Create a Reference element, including the (optional) identification of the data object, any (optional) transform elements, the digest algorithm and the DigestValue. (Note, it is the canonical form of these references that are signed in 3.1.2 and validated in 3.2.1 .)

3.1.2 Signature Generation

1. Create SignedInfo element with SignatureMethod, CanonicalizationMethod and Reference(s).

2. Canonicalize and then calculate the SignatureValue over SignedInfo based on algorithms specified in SignedInfo.

3. Construct the Signature element that includes SignedInfo, Object(s) (if desired, encoding may be different than that used for signing), KeyInfo (if required), and SignatureValue.

get_google_form

This function will give you a complete HTML page that you can send to clients to have them redirected to Google. Note that former versions of this module also included a Content-Type HTTP header. Fortunately, this is no longer the case and you will have to send a "Content-Type: text/html" yourself using whatever method your framework provides.

After all the hi-tec stuff Google wants us to do to parse their request and generate a response, this is where it gets low-tec and messy. We are supposed to give clients a html page that contains a hidden form that uses Javascript to post that form to Google. Ugly, but it works. The form will contain a textarea containing the response xml and a textarea containing the relay state.

Hence the only required argument: the RelayState parameter from the user's GET request

REMARKS

Coming up with a valid response for a SAML-request is quite tricky. The simplest way to go is to use the xmlsec1 program distributed with the XML Security Library. Google seems to use that program itself. However, I wanted to have a perlish way of creating the response. Testing your computed response is best done against xmlsec1: If your response is stored in the file test.xml, you can simply do:

 xmlsec1 --verify --store-references --store-signatures test.xml > debug.txt

This will give you a file debug.txt with lots of information, most importantly it will give you the canonical xml versions of your response and the 'References' element. If your canonical xml of these two elements isn't exactly like the one in debug.txt, your response will not be valid.

This brings us to another issue: XML-canonicalization. There are currently two modules on CPAN that promise to do the work for you: XML::CanonicalizeXML and XML::Canonical. Both can be used with Google::SAML::Response, however the default is to use the former because it is much easier to install. However, the latter's interface is much cleaner and Perl-like than the interface of the former.

XML::Canonical uses XML::GDOME which has a Makefile.PL that begs to be hacked because it insists on using the version of gdome that was available when Makefile.PL was written (2003) and then it still doesn't install without force. XML::CanonicalizeXML is much easier to install, you just have to have the libxml development files installed so it will compile.

TODO

•: Add support for encrypted keys

SOURCE CODE

This module has a github repository:

  https://github.com/mannih/Google-SAML-Response/

AUTHOR

Manni Heumann (saml at lxxi dot org)

with the help of Jeremy Smith and Thiago Damasceno. Thank you!

LICENSE

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.