OAuth2 offers a clear differentiation between token grants and token types. Grant is what Access Token service will verify before issuing a token, and the best thing about it is that the same code path is used irrespectively of whatever grant or token is used.
OAuth2 mentions simple bearer tokens as default token types, but of course the bearer is not the only token type possible.
Eran Hammer-Lahav wrote a MAC Access Authentication draft which introduces a MAC authentication scheme and describes how it can be used in OAuth2.
OAuth2 experts are considering whether this effort has to be completed or not. I'd like to encourage those who are interested to check OAuth2 mail archives for different opinions expressed regarding the MAC scheme.
Here is my opinion for whatever it is worth:
- What is important is that OAuth2 offers a pluggable mechanism for different token types so I think users should be encouraged to experiment with new token types, MAC in this case, and see if it makes the flows more secure, and 'contribute' to the idea of completing the effort from Eran by talking about possible issues or advantages of this scheme (such as: is it simpler to operate than tokens like JWT, or is it a reasonable alternative to JWT, etc) - remember, it is still the same code path for client and server applications, only a different token type.
- Having it completed will encourage OAuth1.0 users migrate to OAuth2.0, because OAuth2.0 with MAC is a much simpler version of OAuth1.0 - MAC scheme offers a simple holder-of-key support and combined with HTTPS it makes the exchanges between clients and OAuth2 services more secure.
- It will be a good idea to complete the effort any way, some implementers will ignore it but some will like.
Sasi M. has contributed the initial MAC Token implementation to Apache CXF, thanks! The documentation is available here. Please try this token type in the applications, it is really easy to work with. Also, we'd be open to contributing the MAC-specific code to a dedicated 3rd party module if it will be useful to have the one - the details can be discussed at the CXF dev list. That said - it is just a couple of utility classes that are needed to get a MAC token created and validated. Sasi also provided a patch for a MAC nonce validator - this is not at the trunk yet but will make it there in time.