From 578cb05f7b160bffa432a9c6b1e571744a01b660 Mon Sep 17 00:00:00 2001
From: "m.nabokikh" <maksim.nabokikh@flant.com>
Date: Sun, 5 Dec 2021 23:45:52 +0400
Subject: [PATCH] fix: return invalid_grant error on claiming token of another
 client

Signed-off-by: m.nabokikh <maksim.nabokikh@flant.com>
---
 server/refreshhandlers.go |  4 ++-
 server/server_test.go     | 55 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)

diff --git a/server/refreshhandlers.go b/server/refreshhandlers.go
index 8ea7ea9e..2bec0b30 100644
--- a/server/refreshhandlers.go
+++ b/server/refreshhandlers.go
@@ -76,7 +76,9 @@ func (s *Server) getRefreshTokenFromStorage(clientID string, token *internal.Ref
 
 	if refresh.ClientID != clientID {
 		s.logger.Errorf("client %s trying to claim token for client %s", clientID, refresh.ClientID)
-		return nil, invalidErr
+		// According to https://datatracker.ietf.org/doc/html/rfc6749#section-5.2 Dex should response with the
+		//  invalid grant error if token has already been claimed by another client.
+		return nil, &refreshError{msg: errInvalidGrant, desc: invalidErr.desc, code: http.StatusBadRequest}
 	}
 
 	if refresh.Token != token.Token {
diff --git a/server/server_test.go b/server/server_test.go
index 6f4bcb81..12130dfa 100644
--- a/server/server_test.go
+++ b/server/server_test.go
@@ -481,6 +481,47 @@ func makeOAuth2Tests(clientID string, clientSecret string, now func() time.Time)
 					return nil
 				},
 			},
+			{
+				name:   "refresh with different client id",
+				scopes: []string{"openid", "email"},
+				handleToken: func(ctx context.Context, p *oidc.Provider, config *oauth2.Config, token *oauth2.Token, conn *mock.Callback) error {
+					v := url.Values{}
+					v.Add("client_id", clientID)
+					v.Add("client_secret", clientSecret)
+					v.Add("grant_type", "refresh_token")
+					v.Add("refresh_token", "existedrefrestoken")
+					v.Add("scope", "oidc email")
+					resp, err := http.PostForm(p.Endpoint().TokenURL, v)
+					if err != nil {
+						return err
+					}
+
+					defer resp.Body.Close()
+					if resp.StatusCode != http.StatusBadRequest {
+						return fmt.Errorf("expected status code %d, got %d", http.StatusBadRequest, resp.StatusCode)
+					}
+
+					var respErr struct {
+						Error       string `json:"error"`
+						Description string `json:"error_description"`
+					}
+
+					if err = json.NewDecoder(resp.Body).Decode(&respErr); err != nil {
+						return fmt.Errorf("cannot decode token response: %v", err)
+					}
+
+					if respErr.Error != errInvalidGrant {
+						return fmt.Errorf("expected error %q, got %q", errInvalidGrant, respErr.Error)
+					}
+
+					expectedMsg := "Refresh token is invalid or has already been claimed by another client."
+					if respErr.Description != expectedMsg {
+						return fmt.Errorf("expected error description %q, got %q", expectedMsg, respErr.Description)
+					}
+
+					return nil
+				},
+			},
 			{
 				// This test ensures that the connector.RefreshConnector interface is being
 				// used when clients request a refresh token.
@@ -792,6 +833,13 @@ func TestOAuth2CodeFlow(t *testing.T) {
 				t.Fatalf("failed to create client: %v", err)
 			}
 
+			if err := s.storage.CreateRefresh(storage.RefreshToken{
+				ID:       "existedrefrestoken",
+				ClientID: "unexcistedclientid",
+			}); err != nil {
+				t.Fatalf("failed to create existed refresh token: %v", err)
+			}
+
 			// Create the OAuth2 config.
 			oauth2Config = &oauth2.Config{
 				ClientID:     client.ID,
@@ -1570,6 +1618,13 @@ func TestOAuth2DeviceFlow(t *testing.T) {
 					t.Fatalf("failed to create client: %v", err)
 				}
 
+				if err := s.storage.CreateRefresh(storage.RefreshToken{
+					ID:       "existedrefrestoken",
+					ClientID: "unexcistedclientid",
+				}); err != nil {
+					t.Fatalf("failed to create existed refresh token: %v", err)
+				}
+
 				// Grab the issuer that we'll reuse for the different endpoints to hit
 				issuer, err := url.Parse(s.issuerURL.String())
 				if err != nil {