feat: sanitize external identity provider user data (#681)

* feat: sanitize external user data

* remove config option to disable Sanitization: sanitize_external_user_data

* cleanup

---------

Co-authored-by: Christoph Haas <christoph.h@sprinternet.at>

internal/app/auth/sanitize_log_test.go

@@ -0,0 +1,90 @@
+package auth
+
+import (
+	"bytes"
+	"encoding/json"
+	"log/slog"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"pgregory.net/rapid"
+
+	"github.com/h44z/wg-portal/internal/config"
+	"github.com/h44z/wg-portal/internal/domain"
+	"github.com/h44z/wg-portal/internal/testutil"
+)
+
+// captureWarnLogsInline redirects the default slog logger to a buffer, calls fn,
+// restores the original logger, and returns the captured log records.
+func captureWarnLogsInline(fn func()) []map[string]any {
+	original := slog.Default()
+	var buf bytes.Buffer
+	handler := slog.NewJSONHandler(&buf, &slog.HandlerOptions{Level: slog.LevelWarn})
+	slog.SetDefault(slog.New(handler))
+
+	fn()
+
+	slog.SetDefault(original)
+
+	var records []map[string]any
+	decoder := json.NewDecoder(&buf)
+	for decoder.More() {
+		var rec map[string]any
+		if err := decoder.Decode(&rec); err == nil {
+			records = append(records, rec)
+		}
+	}
+	return records
+}
+
+// Property 7: Sanitization change logging completeness
+func TestPropertySanitizationChangeLoggingCompleteness(t *testing.T) {
+	mapping := makeOauthFieldMapping()
+	adminMapping := &config.OauthAdminMapping{}
+
+	rapid.Check(t, func(t *rapid.T) {
+		sub := rapid.StringMatching(`[a-zA-Z0-9_@.-]{1,50}`).Draw(t, "sub")
+		email := rapid.String().Draw(t, "email")
+		firstname := rapid.String().Draw(t, "firstname")
+		lastname := rapid.String().Draw(t, "lastname")
+		phone := rapid.String().Draw(t, "phone")
+		department := rapid.String().Draw(t, "department")
+
+		if sub == "" {
+			sub = "testuser"
+		}
+
+		raw := makeOauthRaw(sub, email, firstname, lastname, phone, department)
+
+		// Count how many fields will actually change after sanitization
+		expectedChanges := 0
+		if domain.SanitizeIdentifier(sub, 256) != sub {
+			expectedChanges++
+		}
+		if domain.SanitizeEmail(email, 254) != email {
+			expectedChanges++
+		}
+		if domain.SanitizeString(firstname, 128) != firstname {
+			expectedChanges++
+		}
+		if domain.SanitizeString(lastname, 128) != lastname {
+			expectedChanges++
+		}
+		if domain.SanitizePhone(phone, 50) != phone {
+			expectedChanges++
+		}
+		if domain.SanitizeString(department, 128) != department {
+			expectedChanges++
+		}
+
+		var records []map[string]any
+		records = captureWarnLogsInline(func() {
+			_, _ = parseOauthUserInfo(mapping, adminMapping, raw, "oauth", "test-provider")
+		})
+
+		actualWarnCount := testutil.CountWarnEntries(records)
+		require.Equal(t, expectedChanges, actualWarnCount,
+			"number of WARN log entries (%d) must equal number of fields changed by sanitization (%d)",
+			actualWarnCount, expectedChanges)
+	})
+}