Function certs 

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

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

Return an iterator over certificates from rd.

Filters out any PEM sections that are not certificates and yields errors if a problem occurs while trying to extract a certificate.