函数 verify_tls12_signature 

pub fn verify_tls12_signature(
    message: &[u8],
    cert: &CertificateDer<'_>,
    dss: &DigitallySignedStruct,
    supported_schemes: &WebPkiSupportedAlgorithms,
) -> Result<HandshakeSignatureValid, Error>

验证 一个 message signature using the cert 公钥 并 any supported scheme.

This function verifies the dss signature over message using the subject 公钥 从 cert。 Since TLS 1.2 doesn’t provide enough information 到 map the dss.scheme into 一个 single SignatureVerificationAlgorithm, 此函数 will map 到 several candidates 并 try each in succession until one succeeds 或 we exhaust all candidates.

，请参见WebPkiSupportedAlgorithms::mapping 以获取更多信息。