I’m writing to highly recommend the article “How to link an application protocol to an OpenID Federation 1.0 trust layer” by Vladimir Dzhuvinov. In it, he defines two kinds of integrity for Federations, and describes how to achieve them:
- Federation Integrity, which is defined as:
- Metadata Integrity, which is defined as:
This ensures mutual trust between two entities is established always from a common trust anchor. Any resolved metadata and policies that govern the client application and the OpenID provider in a transaction will then fall under the rules of the same federation and thus will be aligned and consistent with one another.
It ensures the trust chains for an entity to a given trust anchor will invariably result in consistent metadata and policies. The natural way to achieve this is for the federation topology under a trust anchor to form a tree. Topologies that lead to multiple paths from a leaf entity to a trust anchor are to be avoided.
The article also explores how application protocols, such as OpenID Connect or digital wallet protocols, can achieve those properties in practice (and when they do and don’t need to).
Finally, I’ll note that, as a result of Vladimir’s and others’ thinking about the topic, we just added a section on Federation Topologies to the OpenID Federation specification, which provides concrete guidance on how to achieve Metadata Integrity.
I’ll stop here so as not to repeat all the useful content in Vladimir’s article. By all means, give it read!
