Web SSO with Symfony and SimpleSAMLphp

1. Single sign on (SSO)

Sooner or later web development teams face one problem: you have developed an application at domain X and now you want your new application at domain Y to use the same login information as the other domain. In fact, you want more: you want users who are already logged-in at domain X to be already logged-in at domain Y. This is what SSO is all about. (source: https://auth0.com/blog/what-is-and-how-does-single-sign-on-work )

2. Concepts:

Identity Provider (IdP)  - is responsible for (a) providing identifiers for users looking to interact with a system, (b) asserting to such a system that such an identifier presented by a user is known to the provider, and (c) possibly providing other information about the user that is known to the provider.

ServiceProvider (SP) - it can be any application. In order to access the secure areas of the application the user need to be authenticated and authorized by a IdP

SAML  - Security Assertion Markup Language (SAML, pronounced sam-el) is an XML-based, open-standard data format for exchanging authentication and authorization data between parties, in particular, between an identity provider and a service provider. SAML is a product of the OASIS Security Services Technical Committee.

3. The flow

- the USER  requests a secure area from ServiceProvider

- if the user is not authenticated it is redirected to IdP with some information about SP

- the USER fills his credentials on IdP and after successful authentication is redirected back to SP

- based on the answer from IdP the SP creates the a new user or identify an existing one in his own database and creates a session.

4. Tools

SimpleSAMLphp - it can be used both as IdP and SP, I will be using it only as IdP

lightsaml/SP-Bundle - Symfony Bundle implementing the ServiceProvider

5. Implementation

5.1. Create and configure IdP

Install simpleSAMLphp following the documentation. I've created a virtualhost idp.local and the simpleSAMLphp is available at : http://idp.local/simplesamlphp

Next step is to configure simleSAMLphp as IdentityProvider following the quick guide using the exampleauth:UserPass authentication method.

I'll modify the defined users in config/authsources.php, by replacing the attribute "eduPersonAffilication" with 'roles':

      'student:studentpass' => array(

             'uid' => array('student'),

             'roles' => array('ROLE_USER', 'ROLE_SEF'),

         ),

To make it clear, you have just created a user "student" with password "studentpass". 

Skip the step 6 from the quick guide.

At the step 7 you need to enter the information about ServiceProviders. At this moment they do not exist, but they will, so you can fill the following 2 service providers:

$metadata['http://consumer1.local/saml'] = array(

    'AssertionConsumerService' => 'http://consumer1.local/app_dev.php/saml/login_check',

    'SingleLogoutService'      => 'https://consumer1.local/app_dev.php/logout',

    'simplesaml.nameidattribute' => 'uid',

);

$metadata['http://consumer2.local/saml'] = array(

    'AssertionConsumerService' => 'http://consumer2.local/app_dev.php/saml/login_check',

    'SingleLogoutService'      => 'https://consumer2.local/app_dev.php/logout',

    'simplesaml.nameidattribute' => 'uid',

);

I called them consumers because they consume the authentication service provided by IdP.

Skip steps from 8 to 11.

5.2 Create and configure SPs

Install Symfony and create a virtual host consumer1.local

We will be following the lightsaml/SP-Bundle documentation found here.

At step 7 configure your own entity_id and use the previously created IdP.

 -  First go to your IdP, it should be idp.local/simplesamlphp. Click on the Federation tab, you should see somewhere  SAML 2.0 IdP Metadata. Click on [Show metadata], copy the XML and createa file in your Symfony app: /src/AppBundle/Idp/idp.local.xml and paste the XML.

-  edit app/config.yml

At step 9 (and 11), please see below my security.yml:

Where /secure is a  just route I created for testing purpose. 

Step 10. Basically if the user logged in IdP does not exist in the database of the SP, in this case consumer1.local, it needs to be created.  For this reason a UserCreator class is made. In the documentation this class is able to identify the user id (uid) using a "username mapper" service. I will enhance that by adding an "attributes" mapper which will create an array with the other attributes passed from IdentityProvider. I want to pass a list of roles from IdP to SP.  If you remember I've added a list of 'roles' to my 'student' user. Below you can find a gist with the code for the AttributeMapper

Declare the attribute mapper service in app/services.yml:

attribute_mapper:

   class: AppBundle\Security\User\AttributeMapper

Modify the UserCreator class:

Declare the User Creator service injecting in it our Attribute Mapper service:

    user_creator:
        class: AppBundle\Security\User\UserCreator
        arguments:
            - "@=service('doctrine').getManager()"
            - "@lightsaml_sp.username_mapper.simple"
            - "@inno.attribute_mapper"
Also inject the attribute mapper service into the security.authentication.provider.lightsaml_sp service:

    security.authentication.provider.lightsaml_sp:
        class: LightSaml\SpBundle\Security\Authentication\Provider\LightsSamlSpAuthenticationProvider
        arguments:
            - ~ # provider key
            - ~ # user provider
            - ~ # force
            - "@security.user_checker"
            - "@lightsaml_sp.username_mapper.simple" # username mapper
            - ~ # user creator
            - "@inno.attribute_mapper" # attribute mapper
            - ~ # token factory
        abstract: true





5.3 Put your application at work


In browser try to access consumer1.local/app_dev.php/secure, because you are not   authenticated

 you should be redirected to http://consumer1.local/app_dev.php/saml/discoveryClick on your IdP,

 you will be redirected to the IdP site where you will fill your user and password (student and 

studentpass. After that you are redirected to the secure page on cosumer1.local.You can check your

 database to see the newly created user. Now copy your Symfony installation and make another 

virtual host consumer2.local. Open the browser and try to access:  consumer2.local/app_dev.php/securePick

 your IdP from discovery page, because you are already logged on IdP you will not be asked for 

password again, instead you are redirected to the secure page. Victory!In the next blog post I will

 investigate integrating LDAP with SimpleSAMLphp.