Add Vertex service account support

backend/internal/service/gemini_token_provider.go

@@ -15,7 +15,7 @@ const (
 	geminiTokenCacheSkew   = 5 * time.Minute
 )
 
-// GeminiTokenProvider manages access_token for Gemini OAuth accounts.
+// GeminiTokenProvider manages access_token for Gemini OAuth and Vertex service account accounts.
 type GeminiTokenProvider struct {
 	accountRepo        AccountRepository
 	tokenCache         GeminiTokenCache
@@ -53,8 +53,11 @@ func (p *GeminiTokenProvider) GetAccessToken(ctx context.Context, account *Accou
 	if account == nil {
 		return "", errors.New("account is nil")
 	}
-	if account.Platform != PlatformGemini || account.Type != AccountTypeOAuth {
-		return "", errors.New("not a gemini oauth account")
+	if account.Platform != PlatformGemini || (account.Type != AccountTypeOAuth && account.Type != AccountTypeServiceAccount) {
+		return "", errors.New("not a gemini oauth or service account")
+	}
+	if account.Type == AccountTypeServiceAccount {
+		return p.getServiceAccountAccessToken(ctx, account)
 	}
 
 	cacheKey := GeminiTokenCacheKey(account)
@@ -168,7 +171,51 @@ func (p *GeminiTokenProvider) GetAccessToken(ctx context.Context, account *Accou
 	return accessToken, nil
 }
 
+func (p *GeminiTokenProvider) getServiceAccountAccessToken(ctx context.Context, account *Account) (string, error) {
+	key, err := parseVertexServiceAccountKey(account)
+	if err != nil {
+		return "", err
+	}
+	cacheKey := vertexServiceAccountCacheKey(account, key)
+
+	if p.tokenCache != nil {
+		if token, err := p.tokenCache.GetAccessToken(ctx, cacheKey); err == nil && strings.TrimSpace(token) != "" {
+			return token, nil
+		}
+	}
+
+	locked := false
+	if p.tokenCache != nil {
+		var lockErr error
+		locked, lockErr = p.tokenCache.AcquireRefreshLock(ctx, cacheKey, 30*time.Second)
+		if lockErr == nil && locked {
+			defer func() { _ = p.tokenCache.ReleaseRefreshLock(ctx, cacheKey) }()
+		} else if lockErr != nil {
+			slog.Warn("vertex_service_account_token_lock_failed", "account_id", account.ID, "error", lockErr)
+		} else {
+			time.Sleep(200 * time.Millisecond)
+			if token, err := p.tokenCache.GetAccessToken(ctx, cacheKey); err == nil && strings.TrimSpace(token) != "" {
+				return token, nil
+			}
+		}
+	}
+
+	accessToken, ttl, err := exchangeVertexServiceAccountToken(ctx, key)
+	if err != nil {
+		return "", err
+	}
+	if p.tokenCache != nil {
+		_ = p.tokenCache.SetAccessToken(ctx, cacheKey, accessToken, ttl)
+	}
+	return accessToken, nil
+}
+
 func GeminiTokenCacheKey(account *Account) string {
+	if account != nil && account.Type == AccountTypeServiceAccount {
+		if key, err := parseVertexServiceAccountKey(account); err == nil {
+			return vertexServiceAccountCacheKey(account, key)
+		}
+	}
 	projectID := strings.TrimSpace(account.GetCredential("project_id"))
 	if projectID != "" {
 		return "gemini:" + projectID