acme: add AccountKeyRollover

acme/acme.go

@@ -306,6 +306,20 @@ func (c *Client) UpdateReg(ctx context.Context, acct *Account) (*Account, error)
 	return c.updateRegRFC(ctx, acct)
 }
 
+// AccountKeyRollover attempts to transition a client's account key to a new key.
+// On success client's Key is updated which is not concurrency safe.
+// On failure an error will be returned.
+// The new key is already registered with the ACME provider if the following is true:
+//  - error is of type acme.Error
+//  - StatusCode should be 409 (Conflict)
+//  - Location header will have the KID of the associated account
+//
+// More about account key rollover can be found at
+// https://tools.ietf.org/html/rfc8555#section-7.3.5.
+func (c *Client) AccountKeyRollover(ctx context.Context, newKey crypto.Signer) error {
+	return c.accountKeyRollover(ctx, newKey)
+}
+
 // Authorize performs the initial step in the pre-authorization flow,
 // as opposed to order-based flow.
 // The caller will then need to choose from and perform a set of returned

acme/jws.go

@@ -33,6 +33,10 @@ const noKeyID = KeyID("")
 // See https://tools.ietf.org/html/rfc8555#section-6.3 for more details.
 const noPayload = ""
 
+// noNonce indicates that the nonce should be omitted from the protected header.
+// See jwsEncodeJSON for details.
+const noNonce = ""
+
 // jsonWebSignature can be easily serialized into a JWS following
 // https://tools.ietf.org/html/rfc7515#section-3.2.
 type jsonWebSignature struct {
@@ -45,10 +49,15 @@ type jsonWebSignature struct {
 // The result is serialized in JSON format containing either kid or jwk
 // fields based on the provided KeyID value.
 //
-// If kid is non-empty, its quoted value is inserted in the protected head
+// The claimset is marshalled using json.Marshal unless it is a string.
+// In which case it is inserted directly into the message.
+//
+// If kid is non-empty, its quoted value is inserted in the protected header
 // as "kid" field value. Otherwise, JWK is computed using jwkEncode and inserted
 // as "jwk" field value. The "jwk" and "kid" fields are mutually exclusive.
 //
+// If nonce is non-empty, its quoted value is inserted in the protected header.
+//
 // See https://tools.ietf.org/html/rfc7515#section-7.
 func jwsEncodeJSON(claimset interface{}, key crypto.Signer, kid KeyID, nonce, url string) ([]byte, error) {
 	if key == nil {
@@ -58,20 +67,36 @@ func jwsEncodeJSON(claimset interface{}, key crypto.Signer, kid KeyID, nonce, ur
 	if alg == "" || !sha.Available() {
 		return nil, ErrUnsupportedKey
 	}
-	var phead string
+	headers := struct {
+		Alg   string          `json:"alg"`
+		KID   string          `json:"kid,omitempty"`
+		JWK   json.RawMessage `json:"jwk,omitempty"`
+		Nonce string          `json:"nonce,omitempty"`
+		URL   string          `json:"url"`
+	}{
+		Alg:   alg,
+		Nonce: nonce,
+		URL:   url,
+	}
 	switch kid {
 	case noKeyID:
 		jwk, err := jwkEncode(key.Public())
 		if err != nil {
 			return nil, err
 		}
-		phead = fmt.Sprintf(`{"alg":%q,"jwk":%s,"nonce":%q,"url":%q}`, alg, jwk, nonce, url)
+		headers.JWK = json.RawMessage(jwk)
 	default:
-		phead = fmt.Sprintf(`{"alg":%q,"kid":%q,"nonce":%q,"url":%q}`, alg, kid, nonce, url)
+		headers.KID = string(kid)
+	}
+	phJSON, err := json.Marshal(headers)
+	if err != nil {
+		return nil, err
 	}
-	phead = base64.RawURLEncoding.EncodeToString([]byte(phead))
+	phead := base64.RawURLEncoding.EncodeToString([]byte(phJSON))
 	var payload string
-	if claimset != noPayload {
+	if val, ok := claimset.(string); ok {
+		payload = val
+	} else {
 		cs, err := json.Marshal(claimset)
 		if err != nil {
 			return nil, err

acme/jws_test.go

@@ -195,6 +195,44 @@ func TestJWSEncodeJSON(t *testing.T) {
 	}
 }
 
+func TestJWSEncodeNoNonce(t *testing.T) {
+	kid := KeyID("https://example.org/account/1")
+	claims := "RawString"
+	const (
+		// {"alg":"ES256","kid":"https://example.org/account/1","nonce":"nonce","url":"url"}
+		protected = "eyJhbGciOiJFUzI1NiIsImtpZCI6Imh0dHBzOi8vZXhhbXBsZS5vcmcvYWNjb3VudC8xIiwidXJsIjoidXJsIn0"
+		// "Raw String"
+		payload = "RawString"
+	)
+
+	b, err := jwsEncodeJSON(claims, testKeyEC, kid, "", "url")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var jws struct{ Protected, Payload, Signature string }
+	if err := json.Unmarshal(b, &jws); err != nil {
+		t.Fatal(err)
+	}
+	if jws.Protected != protected {
+		t.Errorf("protected:\n%s\nwant:\n%s", jws.Protected, protected)
+	}
+	if jws.Payload != payload {
+		t.Errorf("payload:\n%s\nwant:\n%s", jws.Payload, payload)
+	}
+
+	sig, err := base64.RawURLEncoding.DecodeString(jws.Signature)
+	if err != nil {
+		t.Fatalf("jws.Signature: %v", err)
+	}
+	r, s := big.NewInt(0), big.NewInt(0)
+	r.SetBytes(sig[:len(sig)/2])
+	s.SetBytes(sig[len(sig)/2:])
+	h := sha256.Sum256([]byte(protected + "." + payload))
+	if !ecdsa.Verify(testKeyEC.Public().(*ecdsa.PublicKey), h[:], r, s) {
+		t.Error("invalid signature")
+	}
+}
+
 func TestJWSEncodeKID(t *testing.T) {
 	kid := KeyID("https://example.org/account/1")
 	claims := struct{ Msg string }{"Hello JWS"}

acme/rfc8555.go

@@ -148,6 +148,42 @@ func responseAccount(res *http.Response) (*Account, error) {
 	}, nil
 }
 
+// accountKeyRollover attempts to perform account key rollover.
+// On success it will change client.Key to the new key.
+func (c *Client) accountKeyRollover(ctx context.Context, newKey crypto.Signer) error {
+	dir, err := c.Discover(ctx) // Also required by c.accountKID
+	if err != nil {
+		return err
+	}
+	kid := c.accountKID(ctx)
+	if kid == noKeyID {
+		return ErrNoAccount
+	}
+	oldKey, err := jwkEncode(c.Key.Public())
+	if err != nil {
+		return err
+	}
+	payload := struct {
+		Account string          `json:"account"`
+		OldKey  json.RawMessage `json:"oldKey"`
+	}{
+		Account: string(kid),
+		OldKey:  json.RawMessage(oldKey),
+	}
+	inner, err := jwsEncodeJSON(payload, newKey, noKeyID, noNonce, dir.KeyChangeURL)
+	if err != nil {
+		return err
+	}
+
+	res, err := c.post(ctx, nil, dir.KeyChangeURL, base64.RawURLEncoding.EncodeToString(inner), wantStatus(http.StatusOK))
+	if err != nil {
+		return err
+	}
+	defer res.Body.Close()
+	c.Key = newKey
+	return nil
+}
+
 // AuthorizeOrder initiates the order-based application for certificate issuance,
 // as opposed to pre-authorization in Authorize.
 // It is only supported by CAs implementing RFC 8555.

acme/rfc8555_test.go

@@ -232,13 +232,15 @@ func (s *acmeServer) start() {
 				"newOrder": %q,
 				"newAuthz": %q,
 				"revokeCert": %q,
+				"keyChange": %q,
 				"meta": {"termsOfService": %q}
 				}`,
 				s.url("/acme/new-nonce"),
 				s.url("/acme/new-account"),
 				s.url("/acme/new-order"),
 				s.url("/acme/new-authz"),
 				s.url("/acme/revoke-cert"),
+				s.url("/acme/key-change"),
 				s.url("/terms"),
 			)
 			return
@@ -621,6 +623,27 @@ func TestRFC_GetRegOtherError(t *testing.T) {
 	}
 }
 
+func TestRFC_AccountKeyRollover(t *testing.T) {
+	s := newACMEServer()
+	s.handle("/acme/new-account", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Location", s.url("/accounts/1"))
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(`{"status": "valid"}`))
+	})
+	s.handle("/acme/key-change", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+	s.start()
+	defer s.close()
+
+	cl := &Client{Key: testKeyEC, DirectoryURL: s.url("/")}
+	if err := cl.AccountKeyRollover(context.Background(), testKeyEC384); err != nil {
+		t.Errorf("AccountKeyRollover: %v, wanted no error", err)
+	} else if cl.Key != testKeyEC384 {
+		t.Error("AccountKeyRollover did not rotate the client key")
+	}
+}
+
 func TestRFC_AuthorizeOrder(t *testing.T) {
 	s := newACMEServer()
 	s.handle("/acme/new-account", func(w http.ResponseWriter, r *http.Request) {