if ext.Id.Equal(subjectAltName) {
    var altName asn1.RawValue
    asn1.Unmarshal(ext.Value, &altName)
    if altName.Class == 0 && altName.Tag == 16 {
        data := altName.Bytes
        for len(data) > 0 {
              var alt asn1.RawValue
              data, _ = asn1.Unmarshal(data, &alt)
              if alt.Class == 2 {
                  switch (alt.Tag) {
                  case 0:
                      ...
                  }
              }
          }
     }
}