K   string `json:"k,omitempty"`
}

var (
	errMalformedJWKRSAKey = errors.New("malformed JWK RSA key")
	errMalformedJWKECKey  = errors.New("malformed JWK EC key")
)

// DecodePublicKey - decodes JSON Web Key (JWK) as public key
func (key *JWKS) DecodePublicKey() (crypto.PublicKey, error) {
	switch key.Kty {
	case "RSA":
		if key.N == "" || key.E == "" {
			return nil, errMalformedJWKRSAKey
		}

		// decode exponent

		t.Fatal("Unmarshal: ", err)
	} else if len(jk.Keys) != 3 {
		t.Fatalf("Expected 3 keys, got %d", len(jk.Keys))
	}

	var kids []string
	for ii, jks := range jk.Keys {
		_, err := jks.DecodePublicKey()
		if err != nil {
			t.Fatalf("Failed to decode key %d: %v", ii, err)
		}
		kids = append(kids, jks.Kid)
	}
	if len(kids) != 3 {
		t.Fatalf("Failed to find the expected number of kids: 3, got %d", len(kids))

}

func (pk *publicKeys) parseAndAdd(b io.Reader) error {
	var jwk JWKS
	err := json.NewDecoder(b).Decode(&jwk)
	if err != nil {
		return err
	}

	for _, key := range jwk.Keys {
		pkey, err := key.DecodePublicKey()
		if err != nil {
			return err
		}
		pk.add(key.Kid, pkey)
	}

	return nil
}

func (pk *publicKeys) add(keyID string, key interface{}) {
	pk.Lock()
	defer pk.Unlock()