The GNAPathon

Our Goals

GNAP is a big protocol, and there was no reasonable way for us to build out literally every piece and option of it in our limited timeframe. While GNAP’s transaction negotiation patterns make the protocol fail gracefully when two sides don’t have matching features, we wanted to aim for success. As a consequence, we decided to focus on a few key interoperability points:

  • HTTP Message Signatures for key proofing, with Content Digest for protecting the body of POST messages.
  • Redirect-based interaction, to get there and back.
  • Dynamic keys, not relying on pre-registration at the AS.
  • Single access tokens.

New Clients

With all of this in hand, we set about building some clients from scratch. Since we had a functioning AS to build against, focusing on the clients allowed us to address different platforms and languages than we otherwise had. We settled on three very different kinds of client software:

Getting Over the Hump

Importantly, we also tried to work in such a way that the different components could be abstracted out after the fact. While we could have written very GNAP-specific code to handle the key handling and signing, we opted to instead create generic functions that could sign and present any HTTP message. This decision had two effects.

Bug Fixes

Another important part of the hackathon was the discovery and patching of bugs in the existing XYZ authorization server and Java Servlet web-based client code. At the beginning of the weekend, these pieces of software worked with each other. However, it became quickly apparent that there were a number of issues and assumptions in the implementation. Finding things like this is one of the best things that can come out of a hackathon — by putting different code from different developers against each other, you can figure out where code is weak, and sometimes, where the specification itself is unclear.

Constructing the Layers

Probably the most valuable outcome of the hackathon, besides the working code itself, is a concrete appreciation of how clear the spec is from the eyes of someone trying to build to it. We came out of the weekend with a number of improvements that need to be made to GNAP and HTTP Message Signatures, but also ideas on what additional developer support there should be in the community at large. These things will be produced and incorporated over time, and hopefully make the GNAP ecosystem brighter and stronger as a result.



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Justin Richer

Justin Richer

Justin Richer is a security architect and freelance consultant living in the Boston area. To get in touch, contact his company: