Introduction to OAuth 2.0, OpenID Connect, and SCIM

The development of SAML dates from January 2001. As discussed in an earlier post, SAML 2.0 provides a Single Sign On (SSO) authentication and authorization protocol that many view as applicable primarily for federations of enterprises. Mobile applications and dominant Internet applications such as Salesforce, Facebook, Google Apps, Linked In, etc. were providing more or less independent and light-weight “micro-services” fronted by APIs. SAML was deemed too heavy-weight to be supported by such APIs.

By 2014, authentication, authorization, and delegation (of authorized rights) for APIs, are embodied in the standards OAuth, OpenID Connect, and SCIM. These standards call for authentication and access tokens encoded in JavaScript-like Object Notation JSON rather than SAML’s (somewhat more verbose) XML. These JSON tokens are then passed in HTTP headers.

OAuth 2.0 has evolved to be a base technology for authorization, but it’s hard to do authorization without knowing to whom or to what you’re giving rights, and thus authentication sneaks in to the standard. To better address this, OpenID Connect has evolved from earlier versions of OpenID and other security work done by vendors to become a layer on top of OAuth 2.0 for authentication. It would seem that these two standards should merge.

While the proponents of OAuth and OpenID Connect predict that they will eventually supersede SAML, this doesn’t seem likely in the near future as SAML seems to do quite well for enterprises with existing relationships such as supply chains and portals. In addition, there are some use cases where the co-existence of SAML, OAuth, and OpenID Connect seems natural in spite of some duplication of functionality.

Finally SCIM, the System for Cross-domain Identity Management, addresses cross-domain identity management and specifically provides REST APIs for provisioning, change, and de-provisioning, all of which lie outside the realm of OAuth and SAML. SCIM adds considerable complexity to identity management systems, and I’m a little nervous that the initial implementations will have security problems. On the other hand, neglecting these functions is probably worse for security.

My next few IAM posts will discuss the latest versions for each of OAuth, OpenID Connect, and SCIM. I’ll also work an example of co-existence with SAML. The OAuth 2.0 post is next. It is here.

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