We've been building oso - an open source policy engine for authorization that's embedded in your application.The core of oso is the Polar language for writing policies, which is a logic programming language implemented in Rust and exposed to a bunch of other languages over FFI + WASM.
We added initial Rust support for oso in v0.6. It was pretty different to the other language integrations we built, and required us implementing a runtime reflection system for Rust to drive interactions between the Polar VM and the Rust applications. We had a ton of fun building it, so we decided to write up our experiences in some blog posts. Here's the first part!
Some other useful links:
Source code: https://github.com/osohq/oso/
Feel free to join us on Slack for any questions: join-slack.osohq.com or ask me here!