a alternative, ( maybe not as nice as a pure rust tls version) may be to use mbedtls. ( This can be run on no_std but needs a allocator)

While the name suggest that it only works on "esp chips" the following [repo](https://github.com/esp-rs/esp-mbedtls) can work technically in any env. Currently it works either on esp-hal, esp-idf-hal or on your host machine. 

E.g it builds a portable version of mbedtls and provides the rust abstraction for you. 

They were talks to rename it from esp-mbedtls to just mbedtls but not sure how far it got. Also i dont think anybody else uses it currently.