serde_derive does not currently support using integer values as map
keys. CTAP uses integer values for various CBOR map keys. In order to
properly serialize and deserialize types for the CTAP protocol, a forked
version of serde from a pull request that adds support for renaming
field keys as integer types is used.
Tracked in <https://github.com/serde-rs/serde/pull/2209>
