Deriving minicbor traits fails on this:

/// Decodes a COSE key such as
/// ```
/// {1: 1, -1: 7}
/// ```
#[derive(minicbor::Decode)]
#[cbor(map)]
pub struct CoseKeyOkpEc2<'a> {
    #[n(1)]
    pub kty: i32,
    #[n(-1)]
    pub crv: Option<i32>,
}

error: expected `u32` value
  --> /home/chrysn/git/crates/ariel-os/src/lib/coapcore/src/ace.rs:97:9
   |
97 |     #[n(-1)]

Having negative keys in CBOR maps is a bit more rare than positive keys, but not completely unheard of: it is present in COSE but also in SenML.

Negative values to b() and n(), when used with the cbor(array) container encoding, make no sense, but I don't think it hurts to raise the error then rather than when processing the n()/b().

I'll try to work on a patch; if it is easier than the workaround, that will come soon; otherwise, whenever I next have a bit of spare time. (Such a patch may even prepare support for mixed integer and text string keys, as also COSE and SenML have it, but so far I haven't needed any of the text keys).