// when picking possible candidates the list is built in the order
	// of match plausibility as to save cycles in buildChains:
	//   AKID and SKID match
	//   AKID present, SKID missing / AKID missing, SKID present
	//   AKID and SKID don't match
	var matchingKeyID, oneKeyID, mismatchKeyID []potentialParent
	for _, c := range s.byName[string(cert.RawIssuer)] {
		candidate, constraint, err := s.cert(c)

				return c
			}(),
			expectedIdentifier: "SN=1, SKID=, AKID=D3:07:CD:72:E6:BE:0A:5A:D8:E9:60:20:AF:C2:F2:36:7E:33:62:0B",
		},
		{
			name: "empty AKID",
			cert: func() *x509.Certificate {
				c := getCert(t, clientCNCert)
				c.AuthorityKeyId = nil
				return c
			}(),
			expectedIdentifier: "SN=1, SKID=FB:77:D6:D0:84:A8:10:DF:FA:4E:A4:E0:F1:2A:BB:B4:80:FD:4F:3F, AKID=",
		},
		{
			name:               "self-signed",

	}
	val := cryptobyte.String(e.Value)
	var akid cryptobyte.String
	if !val.ReadASN1(&akid, cryptobyte_asn1.SEQUENCE) {
		return nil, errors.New("x509: invalid authority key identifier")
	}
	if akid.PeekASN1Tag(cryptobyte_asn1.Tag(0).ContextSpecific()) {
		if !akid.ReadASN1(&akid, cryptobyte_asn1.Tag(0).ContextSpecific()) {
			return nil, errors.New("x509: invalid authority key identifier")

		sb.WriteRune(r)
		if i%2 == 1 && i != len(h)-1 {
			sb.WriteRune(':')
		}
	}
	return sb.String()
}

func certificateIdentifier(c *x509.Certificate) string {
	return fmt.Sprintf(
		"SN=%d, SKID=%s, AKID=%s",
		c.SerialNumber,
		columnSeparatedHex(c.SubjectKeyId),
		columnSeparatedHex(c.AuthorityKeyId),
	)
}

	},
	ErrCredMalformed: {
		Code:           "AuthorizationQueryParametersError",
		Description:    "Error parsing the X-Amz-Credential parameter; the Credential is mal-formed; expecting \"<YOUR-AKID>/YYYYMMDD/REGION/SERVICE/aws4_request\".",
		HTTPStatusCode: http.StatusBadRequest,
	},
	ErrMalformedDate: {
		Code:           "MalformedDate",

		currentTime: 1540000000,
		systemSkip:  true, // does not chain to a system root

		errorCallback: expectHostnameError("certificate relies on legacy Common Name field"),
	},
	{
		// A certificate with an AKID should still chain to a parent without SKID.
		// See Issue 30079.
		name:        "AKIDNoSKID",
		leaf:        leafWithAKID,
		roots:       []string{rootWithoutSKID},
		currentTime: 1550000000,