Function rsa_private_keys 

pub fn rsa_private_keys(
    rd: &mut dyn BufRead,
) -> impl Iterator<Item = Result<PrivatePkcs1KeyDer<'static>, Error>>

Available on (crate features rustls or boring or acme) and crate feature rustls and crate feature std only.

Return an iterator over RSA private keys from rd.

Filters out any PEM sections that are not RSA private keys and yields errors if a problem occurs while trying to extract an RSA private key.