Reason is the last 3 digits of the error code.
// None is a non-specified error. const ( None Reason = iota )
// Parsing errors const ( Unknown Reason = iota // X000 ReadFailed // X001 DecodeFailed // X002
// SelfSigned indicates that a certificate is self-signed and // cannot be used in the manner being attempted. SelfSigned Reason = 100 * (iota + 1) // Code 11XX // VerifyFailed is an X.509 verification failure. The least two