diff --git a/backend/internal/handler/auth_oauth_pending_flow.go b/backend/internal/handler/auth_oauth_pending_flow.go
index c7cd6103..658a5f52 100644
--- a/backend/internal/handler/auth_oauth_pending_flow.go
+++ b/backend/internal/handler/auth_oauth_pending_flow.go
@@ -1290,6 +1290,9 @@ func buildPendingOAuthSessionStatusPayload(session *dbent.PendingAuthSession) gi
 
 func normalizePendingOAuthCompletionResponse(payload map[string]any) map[string]any {
 	normalized := clonePendingMap(payload)
+	for _, key := range []string{"access_token", "refresh_token", "expires_in", "token_type"} {
+		delete(normalized, key)
+	}
 	step := strings.ToLower(strings.TrimSpace(pendingSessionStringValue(normalized, "step")))
 	switch step {
 	case "choice", "choose_account_action", "choose_account", "choose", "email_required", "bind_login_required":
diff --git a/backend/internal/handler/auth_oauth_pending_flow_test.go b/backend/internal/handler/auth_oauth_pending_flow_test.go
index a212eb91..c0413d4d 100644
--- a/backend/internal/handler/auth_oauth_pending_flow_test.go
+++ b/backend/internal/handler/auth_oauth_pending_flow_test.go
@@ -851,6 +851,22 @@ func TestExchangePendingOAuthCompletionBlocksBackendModeBeforeReturningTokenPayl
 	require.Nil(t, storedSession.ConsumedAt)
 }
 
+func TestNormalizePendingOAuthCompletionResponseScrubsLegacyTokenPayload(t *testing.T) {
+	payload := normalizePendingOAuthCompletionResponse(map[string]any{
+		"access_token":  "legacy-access-token",
+		"refresh_token": "legacy-refresh-token",
+		"expires_in":    float64(3600),
+		"token_type":    "Bearer",
+		"redirect":      "/dashboard",
+	})
+
+	require.NotContains(t, payload, "access_token")
+	require.NotContains(t, payload, "refresh_token")
+	require.NotContains(t, payload, "expires_in")
+	require.NotContains(t, payload, "token_type")
+	require.Equal(t, "/dashboard", payload["redirect"])
+}
+
 func TestExchangePendingOAuthCompletionInvitationRequiredFalseFalsePersistsDecisionWithoutBinding(t *testing.T) {
 	handler, client := newOAuthPendingFlowTestHandler(t, true)
 	ctx := context.Background()
diff --git a/backend/internal/service/auth_pending_identity_service.go b/backend/internal/service/auth_pending_identity_service.go
index 26732c77..cc0522ab 100644
--- a/backend/internal/service/auth_pending_identity_service.go
+++ b/backend/internal/service/auth_pending_identity_service.go
@@ -236,6 +236,7 @@ func (s *AuthPendingIdentityService) consumeSession(
 		return nil, err
 	}
 
+	sanitizedLocalFlowState := sanitizePendingAuthLocalFlowState(session.LocalFlowState)
 	now := time.Now().UTC()
 	update := s.entClient.PendingAuthSession.UpdateOneID(session.ID).
 		Where(
@@ -247,6 +248,7 @@ func (s *AuthPendingIdentityService) consumeSession(
 			),
 		).
 		SetConsumedAt(now).
+		SetLocalFlowState(sanitizedLocalFlowState).
 		SetCompletionCodeHash("").
 		ClearCompletionCodeExpiresAt()
 	if expectedBrowserSessionKey := strings.TrimSpace(session.BrowserSessionKey); expectedBrowserSessionKey != "" {
@@ -273,6 +275,29 @@ func (s *AuthPendingIdentityService) consumeSession(
 	return nil, consumedErr
 }
 
+func sanitizePendingAuthLocalFlowState(localFlowState map[string]any) map[string]any {
+	sanitized := copyPendingMap(localFlowState)
+	if len(sanitized) == 0 {
+		return sanitized
+	}
+
+	rawCompletion, ok := sanitized["completion_response"]
+	if !ok {
+		return sanitized
+	}
+	completion, ok := rawCompletion.(map[string]any)
+	if !ok {
+		return sanitized
+	}
+
+	cleanedCompletion := copyPendingMap(completion)
+	for _, key := range []string{"access_token", "refresh_token", "expires_in", "token_type"} {
+		delete(cleanedCompletion, key)
+	}
+	sanitized["completion_response"] = cleanedCompletion
+	return sanitized
+}
+
 func validatePendingSessionState(session *dbent.PendingAuthSession, browserSessionKey string, expiredErr error, consumedErr error) error {
 	if session == nil {
 		return ErrPendingAuthSessionNotFound
diff --git a/backend/migrations/122_pending_auth_completion_token_cleanup.sql b/backend/migrations/122_pending_auth_completion_token_cleanup.sql
new file mode 100644
index 00000000..e6341142
--- /dev/null
+++ b/backend/migrations/122_pending_auth_completion_token_cleanup.sql
@@ -0,0 +1,15 @@
+UPDATE pending_auth_sessions
+SET
+    local_flow_state = jsonb_set(
+        local_flow_state,
+        '{completion_response}',
+        ((local_flow_state -> 'completion_response') - 'access_token' - 'refresh_token' - 'expires_in' - 'token_type'),
+        true
+    )
+WHERE jsonb_typeof(local_flow_state -> 'completion_response') = 'object'
+  AND (
+      (local_flow_state -> 'completion_response') ? 'access_token'
+      OR (local_flow_state -> 'completion_response') ? 'refresh_token'
+      OR (local_flow_state -> 'completion_response') ? 'expires_in'
+      OR (local_flow_state -> 'completion_response') ? 'token_type'
+  );
diff --git a/backend/migrations/123_fix_legacy_auth_source_grant_on_signup_defaults.sql b/backend/migrations/123_fix_legacy_auth_source_grant_on_signup_defaults.sql
new file mode 100644
index 00000000..f6053ef0
--- /dev/null
+++ b/backend/migrations/123_fix_legacy_auth_source_grant_on_signup_defaults.sql
@@ -0,0 +1,39 @@
+WITH migration_110 AS (
+    SELECT applied_at
+    FROM schema_migrations
+    WHERE filename = '110_pending_auth_and_provider_default_grants.sql'
+),
+legacy_provider_defaults AS (
+    SELECT provider_type
+    FROM (
+        VALUES ('email'), ('linuxdo'), ('oidc'), ('wechat')
+    ) AS providers(provider_type)
+    CROSS JOIN migration_110
+    JOIN settings balance
+      ON balance.key = 'auth_source_default_' || providers.provider_type || '_balance'
+    JOIN settings concurrency
+      ON concurrency.key = 'auth_source_default_' || providers.provider_type || '_concurrency'
+    JOIN settings subscriptions
+      ON subscriptions.key = 'auth_source_default_' || providers.provider_type || '_subscriptions'
+    JOIN settings grant_on_signup
+      ON grant_on_signup.key = 'auth_source_default_' || providers.provider_type || '_grant_on_signup'
+    JOIN settings grant_on_first_bind
+      ON grant_on_first_bind.key = 'auth_source_default_' || providers.provider_type || '_grant_on_first_bind'
+    WHERE balance.value = '0'
+      AND concurrency.value = '5'
+      AND subscriptions.value = '[]'
+      AND grant_on_signup.value = 'true'
+      AND grant_on_first_bind.value = 'false'
+      AND balance.updated_at BETWEEN migration_110.applied_at - INTERVAL '1 minute' AND migration_110.applied_at + INTERVAL '1 minute'
+      AND concurrency.updated_at BETWEEN migration_110.applied_at - INTERVAL '1 minute' AND migration_110.applied_at + INTERVAL '1 minute'
+      AND subscriptions.updated_at BETWEEN migration_110.applied_at - INTERVAL '1 minute' AND migration_110.applied_at + INTERVAL '1 minute'
+      AND grant_on_signup.updated_at BETWEEN migration_110.applied_at - INTERVAL '1 minute' AND migration_110.applied_at + INTERVAL '1 minute'
+      AND grant_on_first_bind.updated_at BETWEEN migration_110.applied_at - INTERVAL '1 minute' AND migration_110.applied_at + INTERVAL '1 minute'
+)
+UPDATE settings
+SET
+    value = 'false',
+    updated_at = NOW()
+FROM legacy_provider_defaults
+WHERE settings.key = 'auth_source_default_' || legacy_provider_defaults.provider_type || '_grant_on_signup'
+  AND settings.value = 'true';
diff --git a/backend/migrations/auth_identity_payment_migrations_regression_test.go b/backend/migrations/auth_identity_payment_migrations_regression_test.go
index 988876a9..48cc427b 100644
--- a/backend/migrations/auth_identity_payment_migrations_regression_test.go
+++ b/backend/migrations/auth_identity_payment_migrations_regression_test.go
@@ -59,3 +59,28 @@ func TestMigration119DefersPaymentIndexRolloutToOnlineFollowup(t *testing.T) {
 	require.Contains(t, followupSQL, "DROP INDEX CONCURRENTLY IF EXISTS paymentorder_out_trade_no")
 	require.Contains(t, followupSQL, "WHERE out_trade_no <> ''")
 }
+
+func TestMigration122ScrubsPendingOAuthCompletionTokensAtRest(t *testing.T) {
+	content, err := FS.ReadFile("122_pending_auth_completion_token_cleanup.sql")
+	require.NoError(t, err)
+
+	sql := string(content)
+	require.Contains(t, sql, "UPDATE pending_auth_sessions")
+	require.Contains(t, sql, "completion_response")
+	require.Contains(t, sql, "access_token")
+	require.Contains(t, sql, "refresh_token")
+	require.Contains(t, sql, "expires_in")
+	require.Contains(t, sql, "token_type")
+}
+
+func TestMigration123BackfillsLegacyAuthSourceGrantDefaultsSafely(t *testing.T) {
+	content, err := FS.ReadFile("123_fix_legacy_auth_source_grant_on_signup_defaults.sql")
+	require.NoError(t, err)
+
+	sql := string(content)
+	require.Contains(t, sql, "110_pending_auth_and_provider_default_grants.sql")
+	require.Contains(t, sql, "schema_migrations")
+	require.Contains(t, sql, "updated_at")
+	require.Contains(t, sql, "'_grant_on_signup'")
+	require.Contains(t, sql, "value = 'false'")
+}