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),
	)
}