Function issue_certificate_authority_leaf 

pub fn issue_certificate_authority_leaf(
    ca: &CertificateAuthorityData,
    request: LeafCertRequest,
) -> Result<(Vec<CertificateDer<'static>>, PrivateKeyDer<'static>), Box<dyn Error + Send + Sync>>

Available on crate feature crypto and crate feature std and (crate features aws-lc or ring) only.