x509-cert: How to use dynamic signer with Builder?

Hey 👋🏻

I'm trying to use a dynamic signer when using RequestBuilder, but I'm running into this:

the size for values of type dyn Signer<_> cannot be known at compilation time
the trait Sized is not implemented for dyn Signer<_>

Here's a distillation of what I'm attempting:

use p256::pkcs8::LineEnding;
use rand_core::OsRng;
use std::error::Error;
use std::str::FromStr;
use x509_cert::{builder::RequestBuilder, name::Name};

fn main() -> Result<(), Box<dyn Error>> {
    let req_signer: Box<dyn p256::ecdsa::signature::Signer<_>>;

    if true {
        req_signer = Box::new(p256::ecdsa::SigningKey::random(&mut OsRng));
    } else {
        req_signer = Box::new(p384::ecdsa::SigningKey::random(&mut OsRng));
    }

    let subject = Name::from_str("CN=Test")?;

    let csr_builder = RequestBuilder::new(subject, req_signer.as_ref())?; // <--- Error

    let csr = csr_builder.build::<p256::ecdsa::DerSignature>()?; // <--- p256 or p384 would need to be used here

    let csr_pem = csr.to_pem(LineEnding::LF)?;

    println!("{}", csr_pem);

    Ok(())
}

Does that make sense? Am I just making a stupid mistake, or approaching this in the wrong way?

Thanks for any help!

Start with the RequestBuilder::new and build::<...> entry points shown in the issue, then inspect their signer and signature-type requirements. The payload names no files or tests. Done means establishing and documenting a supported dynamic-signer approach, or clearly confirming the API limitation.