pub fn trust_anchor(self, trust_anchor: TrustAnchor<'static>) -> Self {
        let mut trust_anchors = self.trust_anchors;
        trust_anchors.push(trust_anchor);
        ClientTlsConfig {
            trust_anchors,
            ..self
        }
    }
Adds the trust anchor which to verify the server's TLS certificate.
tonic/src/transport/channel/tls.rs