pub fn fn_chain_append_certificate_entry(
    chain: &Vec<CertificateEntry>,
    cert: &CertificateEntry,
) -> Result<Vec<CertificateEntry>, FnError>pub fn fn_chain_append_certificate_entry(
    chain: &Vec<CertificateEntry>,
    cert: &CertificateEntry,
) -> Result<Vec<CertificateEntry>, FnError>