Monthly Archives September 2012

We’re now a quarter of the way through the Linkey project calendar so I’m going to try and summarise where we are at and where the project is heading.

I’ve spent a considerable amount of time working away on the OAuth PHP library which features code to build an authorisation platform, a resource server, and an abstract client class so that you can easily interact with 3rd party OAuth endpoints.

With this code almost finished and tested I’ve started designing the next generation OAuth endpoint for use here at the university. Coupled with the work we’re doing on the side for our next generation API and open data platform, as well as ICT’s own enterprise service bus and UAG development all together we’re developing a beautiful data driven environment that will allow us to go forth and build rich, personalised and secure services and applications.

My colleagues here in ICT have been testing the UAG on our development network over the past few months and they now feel comfortable to start building a production platform which we can start integrating services into. This will hopefully be ready in the next few weeks and I will be able to go into much more detail about how OAuth and UAG can work together.

The main clients for Linkey are the university library and they have already started reaping some of the benefits of a single sign on environment thanks to an installation of EZProxy which offers reverse proxy authentication to a large number of 3rd party journal and database services. Currently EZProxy is piggybacking off of our Blackboard installation for authentication which benefits students – we know from our analytics that most students access library services through Blackboard – because there are now 35 (at the time of writing) resources which they can access with one click and they won’t have to authenticate a second (or in some cases a third) time.

With a production UAG we should be able to hook up a large percentage of sites and services with relative ease. As a refresher here is the current authentication situation:

https://raw.github.com/lncd/AIM-project/master/SSOCurrentSituation.png

and here is the ideal situation which we should be able to achieve:

https://raw.github.com/lncd/AIM-project/master/SSOIdealSituation.png

Over the next 9 months there are a few other areas of access and identity which I want to cover.

At EduServ’s Federated Access Management conference last year there was a talk by Jonathon Richardson, assistant CIS director at the University of East Anglia where he discussed how students and staff can access some of his institutions’ services with their own 3rd party Internet services accounts (e.g. Facebook/Twitter/Google). I would like to look into what are the benefits and risks associated with allowing staff and students to access university resources with their own accounts instead of the brand new account which they are given by us when they start at the university.

Hopefully the OAuth 2.0 specification will also be completed very soon and I want to further investigate OAuth’s potential use cases. I have submitted a conference talk proposal to ConFoo in Montreal, Canada to discuss my findings.

We have also committed to publishing a case study and organising a workshop about OAuth (and access and identity in general) which we will work with JISC to organise and promote.

EduServ have released a tool they’re calling “Student Access Decision Maker” which makes you answer 9 questions to help you decide if a student, group of students, or students full stop should be able to access a particular resource.

The tool is embedded below:

The OAuth working group have released an initial security review of the OAuth 2.0 specification which looks at a number of potential threats that implementors could face and how to mitigate them.

The document can be read here http://tools.ietf.org/html/draft-tschofenig-oauth-security-00.

The abstract of the document is below:

> The OAuth working group has finished work on the OAuth 2.0 core protocol as well as the Bearer Token specification. The Bearer Tokenis a TLS-based solution for ensuring that neither the interaction with the Authorization Server (when requesting a token) nor the interaction with the Resource Server (for accessing a protected resource) leads to token leakage. There has, however, always been the desire to develop a security solution that is “better” than Bearer Tokens (or at least different) where the Client needs to show
possession of some keying material when accessing a Resource Server.

> This document tries to capture the discussion and to come up with requirements to process the work on solutions.

> This document aims to discuss threats, security requirements and desired design properties of an enhanced OAuth security mechanism.

This afternoon I decided to join the JANET Access and Identity Management group.

I hit the join group button on the site and was then prompted to join the JANET community. Seeing that it supported UK Access Management Federation (UK AMF) sign in, I entered my university’s name and clicked continue.

I was then forwarded to a login screen on the OpenAthens site. I don’t think I have any OpenAthens credentials so I clicked “Alternative login” (but first I accidentally clicked “Forgotten password?” thanks to my haste and the tiny links).

Then I had to choose my institution (again???).

Then I was asked to click on a link to take me to my institution’s login page.

Then I was forwarded onto our current Athens sign-in endpoint where I authenticated with my University of Lincoln network credentials.

Finally I was returned to the JANET Community sign-up screen only to see that none of the form fields had been pre-filled because of course the UK AMF is anonymised.

What a waste of time and a terrible user experience.

One of the outputs of the Linkey project is an open source PHP library that implements the SAML bearer assertion extension (draft 13 at time of writing) to the OAuth 2.0 specification.

But what is SAML?

SAML, or Security Assertion Markup Language, is an XML-based framework that allows identity and security information to be shared across security domains – for example between two websites.

Information is exchanged through the concept of assertion tokens, which are XML documents that state facts about the assertion’s subject. For example, a SAML assertion about me might look like:

<saml:Response ID="_257f9d9e9fa14962c0803903a6ccad931245264310738" IssueInstant="2012-09-03T18:45:10Z" Version="2.0">

    <saml:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">

https://www.lincoln.ac.uk

    </saml:Issuer>

    <saml:Status>
        <saml:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/>
    </saml:Status>

    <saml:Assertion ID="_3c39bc0fe7b13769cab2f6f45eba801b1245264310738" IssueInstant="2012-09-03T18:45:10Z" Version="2.0">
    <saml:Issuer Format="urn:oasis:names:tc:SAML:2.0:nameid-format:entity">

https://www.lincoln.ac.uk

    </saml:Issuer>

    <saml:Subject>
        <saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:unspecified">
            abilbie@lincoln.ac.uk
        </saml:NameID>
        <saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer">
            <saml:SubjectConfirmationData NotOnOrAfter="2012-09-03T18:50:10Z" Recipient="https://sso.lincoln.ac.uk"/>
        </saml:SubjectConfirmation>
    </saml:Subject>

    <saml:Conditions NotBefore="2012-09-03T18:45:10Z" NotOnOrAfter="2012-09-03T18:50:10Z">
        <saml:AudienceRestriction>
            <saml:Audience>https://sso.lincoln.ac.uk</saml:Audience>
        </saml:AudienceRestriction>
    </saml:Conditions>

    <saml:AuthnStatement AuthnInstant="2012-09-03T18:45:10Z">
        <saml:AuthnContext>
            <saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:unspecified</saml:AuthnContextClassRef>
        </saml:AuthnContext>
    </saml:AuthnStatement>

    <saml:AttributeStatement>

        <saml:Attribute Name="name">
            <saml:AttributeValue xsi:type="xs:anyType">Alex Bilbie</saml:AttributeValue>
        </saml:Attribute>

        <saml:Attribute Name="network_id">
            <saml:AttributeValue xsi:type="xs:anyType">abilbie</saml:AttributeValue>
        </saml:Attribute>

        <saml:Attribute Name="division">
            <saml:AttributeValue xsi:type="xs:anyType">ICT Services</saml:AttributeValue>
        </saml:Attribute>

        <saml:Attribute Name="staff_directory_url">
            <saml:AttributeValue xsi:type="xs:anyType">http://staff.lncd.org/abilbie</saml:AttributeValue>
        </saml:Attribute>

    </saml:AttributeStatement>
    </saml:Assertion>
</saml:Response>

This assertion here states that my name is Alex Bilbie, my network ID is abilbie, my division is ICT Services and that my staff directory page is http://staff.lncd.org/abilbie.

Generally the assertion will be provided by an “identity provider” (a.k.a an IDP) and consumed by a “service provider” (a.ka. a SDP).

SAML is often used in single sign on environments. Let’s consider a student trying to sign in to the student union website:

  1. The student (the user) would visit student union website (the SDP)
  2. The SDP would realise the user isn’t yet signed in and so redirects the user to the single sign on endpoint (the IDP)
  3. The user authenticates with the IDP
  4. The IDP redirects the user back to the SDP with the assertion (by using a HTTP POST)
  5. The SDP consumes the assertion, validates it and signs the user in

How does SAML compare to OAuth?

For reference, this is how OAuth is used in a single sign on environment:

  1. The student (the user) would visit student union website (the client)
  2. The client would realise the user isn’t yet signed in and so redirects the user to the single sign on endpoint (the authentication server)
  3. The user authenticates with the authentication server
  4. The user grants the client access to their private data
  5. The authentication server redirects the user back to the client with an authorisation code in the URL
  6. The client exchanges the authorisation code for an access token with the authentication server by itself authenticating
  7. The client then sends a request to the resource server to request the user’s private data. The access token represents permission granted by the user for the client to act on their behalf.

Now the OAuth flow looks longer it contains one important stage which is a requirement of the specification, specifically step 4 which is where the user is explicitly asked if they want to allow the client to access their data and also what data will be accessed. You could emulate this in the SAML flow but I think the upfront honesty so to speak in the OAuth flow is a huge advantage for users. Also most OAuth authentication servers allow users to revoke access to clients as well (i.e. their access token for that client is destroyed which immediately cuts access).

In both flows, the client/SDP itself is verified. In SAML this is done through certificate exchanges, in OAuth the client’s ID is validated at step 3 and step 6.

How does the assertion extension work?

Looking at the OAuth sign-in flow above, at step 6 the client exchanges the authorisation code for an access token. There are a number of ways this can step can actually work and each different method is called an authorisation grant type. The grant described above (and the grant is the generally used in most OAuth implementations) is the authorization_code grant.

The assertion extension defines a new authorisation grant type of urn:ietf:params:oauth:client-assertion-type:saml2-bearer. There is also another parameter called client_assertion which is a base64 encoded representation of the XML assertion. The client/SDP’s own credentials are in the assertion instead of being sent as client_id and client_secret parameters as in the authorisation code grant.

An example request would look like:

POST /token.oauth2 HTTP/1.1
Host: authz.example.net
Content-Type: application/x-www-form-urlencoded

grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Asaml2-
bearer&assertion=PEFzc2VydGlvbiBJc3N1ZUluc3RhbnQ9IjIwMTEtMDU
[...omitted for brevity...]aG5TdGF0ZW1lbnQ-PC9Bc3NlcnRpb24-

The specification includes a number of elements that must be included the assertion in order to provide the authorisation server with all the details it needs about the request.

As I understand it there is also an optional scope parameter that can be passed in the request any scopes that the client/SDP requires.