Route OIDC failures through shared auth error page

A dedicated personal-account page does not scale as more refusal
reasons appear. Redirect the OIDC callback to /auth/error with an
error code query parameter so the frontend can map codes to clear
user-facing messages.

Signed-off-by: Cursor Agent <cursoragent@cursor.com>

Co-authored-by: Bryan FRIMIN <bryan@frimin.fr>

pkg/server/api/connect/v1/auth_error_test.go

@@ -0,0 +1,45 @@
+// Copyright (c) 2026 Probo Inc <hello@probo.com>.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package connect_v1
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRedirectAuthError(t *testing.T) {
+	t.Parallel()
+
+	req := httptest.NewRequest(http.MethodGet, "/api/connect/v1/oidc/google/callback", nil)
+	rec := httptest.NewRecorder()
+
+	redirectAuthError(rec, req, authErrorPersonalAccountNotAllowed)
+
+	assert.Equal(t, http.StatusFound, rec.Code)
+	location, err := rec.Result().Location()
+	require.NoError(t, err)
+	assert.Equal(t, "/auth/error", location.Path)
+	assert.Equal(t, authErrorPersonalAccountNotAllowed, location.Query().Get("error"))
+}