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/domain/user_sanitize_test.go

@@ -0,0 +1,64 @@
+package domain
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/h44z/wg-portal/internal/testutil"
+)
+
+func TestUser_SanitizeExternalData_NullByteInFirstname(t *testing.T) {
+	u := &User{
+		Identifier: "alice",
+		Email:      "alice@example.com",
+		Firstname:  "Ali\x00ce",
+		Lastname:   "Smith",
+	}
+
+	restore := testutil.CaptureWarnLogs(t)
+	err := u.SanitizeExternalData("ldap", "test-provider")
+	records := restore()
+
+	require.NoError(t, err)
+	assert.Equal(t, "Alice", u.Firstname)
+	assert.Equal(t, 1, testutil.CountWarnEntries(records))
+
+	_, found := testutil.FindWarnWithField(records, "firstname")
+	assert.True(t, found)
+}
+
+func TestUser_SanitizeExternalData_IdentifierAll(t *testing.T) {
+	u := &User{
+		Identifier: "all",
+		Email:      "all@example.com",
+		Firstname:  "Alice",
+		Lastname:   "Smith",
+	}
+
+	err := u.SanitizeExternalData("ldap", "test-provider")
+
+	require.Error(t, err)
+	assert.True(t, errors.Is(err, ErrInvalidData))
+}
+
+func TestUser_SanitizeExternalData_AllFieldsClean(t *testing.T) {
+	u := &User{
+		Identifier: "alice",
+		Email:      "alice@example.com",
+		Firstname:  "Alice",
+		Lastname:   "Smith",
+		Phone:      "+1 555-1234",
+		Department: "Engineering",
+	}
+
+	restore := testutil.CaptureWarnLogs(t)
+	err := u.SanitizeExternalData("ldap", "test-provider")
+	records := restore()
+
+	require.NoError(t, err)
+	assert.Equal(t, UserIdentifier("alice"), u.Identifier)
+	assert.Equal(t, 0, testutil.CountWarnEntries(records))
+}