x509: cannot validate certificate for <host ip> because it doesn't contain any IP SANs

I develop a NewRequestWithCert function that create new soap.client and use cert from cert file and after soap.client.Do it returned x509: cannot validate certificate for <host ip> because it doesn't contain any IP SANs. What wrong with my code ?

func (o *Client) NewRequestWithCert(urlLink string, requestData interface{}, responseData interface{}, certName string, host string) error {
// Keep on client
o.requestData = &requestData
o.responseData = &responseData
o.url = urlLink
certByte, errCert := ioutil.ReadFile("/app/certificates/" + certName)
if errCert != nil {
logrus.Errorf("cert err: %v", errCert)
return errCert
}
caCertPool := x509.NewCertPool()
caCertPool.AppendCertsFromPEM(certByte)
logrus.Debug("certByte : ", certByte)
tlsConfig := &tls.Config{
ServerName: host,
ClientCAs:  caCertPool,
ClientAuth: tls.RequireAndVerifyClientCert,
}
// New http client
o.client = &http.Client{
Timeout:   30 * time.Second,
Transport: &http.Transport{
TLSClientConfig: tlsConfig,
},
}
// Make buffer
var requestDataBuffer bytes.Buffer
err := xml.NewEncoder(&requestDataBuffer).Encode(requestData)
logrus.Info("[ProxyRequest] URL: ", urlLink)
logrus.Info("[ProxyRequest] Data: ", requestDataBuffer.String())
// Build a new request, but not doing the POST yet
req, err := http.NewRequest("POST", urlLink, &requestDataBuffer)
if err != nil {
return err
}
// Keep on client
o.req = req
// Fill default header
o.fillHeader()
return nil
}

The subject(s) of the servers certificate do not match the URL you use in your code. Specifically you likely used an IP address for the URL and the server certificate does not contain a Subject Alternative Names extension (SAN) for this IP address (or any other IP address, hence "doesn't contain any IP SANs")

The cause of this mismatch is that you are using a wrong URL or that the server certificate is wrong.

In my case the certificates were provided to me and worked fine with the myslq (MariaDB) command line client. I was even able to create JKS keystores from them to successfully connect through JDBC.
However, my golang code threw this error. My googling led me to https://github.com/prometheus/prometheus/issues/1654#issuecomment-462433443 which gave me a workaround - setting InsecureSkipVerify to true (to skip verification of certificate). Refer to https://godoc.org/crypto/tls#Config for example usage.