I agree with Mark’s commenter who suggests that a SAML attribute service fills the role just as well. Mark suggests that a SAML attribute query is too difficult to implement in some development environments. But I am not sure that I buy the argument that there are environments where doing the SAML SSO is doable but doing the attribute query isn’t.
Regardless all this got me thinking about impedance matching. When we wear our standards hat, all things are possible. But we need to step back at times and put on our developer hat and think about how are designs are going to be implements. While we could mix SAML and OAUTH to support JIT federated provisioning, implementation now requires tools, libraries, and implementers that can implement both SAML and OAUTH as well as handle the rough edges where the don’t mesh well. That’s an impedance mismatch in my opinion.