[Validator] Document the new NoSuspiciousCharacters constraint

Author: MatTheCat

reference/constraints.rst

@@ -79,6 +79,7 @@ Validation Constraints Reference
    constraints/Traverse
    constraints/CssColor
    constraints/Cascade
+   constraints/NoSuspiciousCharacters
 
 The Validator is designed to validate objects against *constraints*.
 In real life, a constraint could be: "The cake must not be burned". In

reference/constraints/NoSuspiciousCharacters.rst

@@ -0,0 +1,157 @@
+NoSuspiciousCharacters
+======================
+
+.. versionadded:: 6.3
+
+    The ``NoSuspiciousCharacters`` constraint was introduced in Symfony 6.3.
+
+..
+
+    Because Unicode contains such a large number of characters and incorporates
+    the varied writing systems of the world, incorrect usage can expose programs
+    or systems to possible security attacks.
+
+    `Unicode® Technical Standard #39`_
+
+"symfony.com" and "ѕymfony.com" look similar, but the latter actually starts with a
+`cyrillic small letter dze`_. It could make a user think they'll navigate to Symfony's
+website, whereas it would be somewhere else.
+This is a kind of `spoofing attack`_ (called "IDN homograph attack"). It tries to
+identify something as something else to exploit the resulting confusion.
+This is why it is recommended to check user-submitted, public-facing identifiers for
+suspicious characters in order to prevent such attacks.
+
+This constraint ensures strings or :phpclass:`Stringable`s do not include any
+suspicious characters. As it leverages PHP's :phpclass:`Spoofchecker`, the intl
+extension must be enabled to use it.
+
+==========  ===================================================================
+Applies to  :ref:`property or method <validation-property-target>`
+Class       :class:`Symfony\\Component\\Validator\\Constraints\\NoSuspiciousCharacters`
+Validator   :class:`Symfony\\Component\\Validator\\Constraints\\NoSuspiciousCharactersValidator`
+==========  ===================================================================
+
+Basic Usage
+-----------
+
+The following constraint will ensures a username cannot be spoofed by using many
+detection mechanisms:
+
+.. configuration-block::
+
+    .. code-block:: php-attributes
+
+        // src/Entity/User.php
+        namespace App\Entity;
+
+        use Symfony\Component\Validator\Constraints as Assert;
+
+        class User
+        {
+            #[Assert\NoSuspiciousCharacters]
+            private string $username;
+        }
+
+    .. code-block:: yaml
+
+        # config/validator/validation.yaml
+        App\Entity\User:
+            properties:
+                username:
+                    - NoSuspiciousCharacters: ~
+
+    .. code-block:: xml
+
+        <!-- config/validator/validation.xml -->
+        <?xml version="1.0" encoding="UTF-8" ?>
+        <constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
+            xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+            xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping https://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">
+
+            <class name="App\Entity\User">
+                <property name="username">
+                    <constraint name="NoSuspiciousCharacters"/>
+                </property>
+            </class>
+        </constraint-mapping>
+
+    .. code-block:: php
+
+        // src/Entity/User.php
+        namespace App\Entity;
+
+        use Symfony\Component\Validator\Constraints as Assert;
+        use Symfony\Component\Validator\Mapping\ClassMetadata;
+
+        class User
+        {
+            public static function loadValidatorMetadata(ClassMetadata $metadata)
+            {
+                $metadata->addPropertyConstraint('username', new Assert\NoSuspiciousCharacters());
+            }
+        }
+
+.. include:: /reference/constraints/_empty-values-are-valid.rst.inc
+
+Options
+-------
+
+``checks``
+~~~~~~~~~~
+
+**type**: ``integer`` **default**: all
+
+This option is a bitmask of the checks you want to perform on the string:
+
+* ``NoSuspiciousCharacters::CHECK_INVISIBLE`` checks for the presence of invisible characters such as zero-width spaces, or character sequences that are likely not to display, such as multiple occurrences of the same non-spacing mark.
+* ``NoSuspiciousCharacters::CHECK_MIXED_NUMBERS`` (usable with ICU 58 or higher) checks for numbers from different numbering systems.
+* ``NoSuspiciousCharacters::CHECK_HIDDEN_OVERLAY`` (usable with ICU 62 or higher) checks for combining characters hidden in their preceding one.
+
+You can also configure additional requirements using :ref:`locales <locales>` and
+:ref:`restrictionLevel <restrictionlevel>`.
+
+``locales``
+~~~~~~~~~~~
+
+**type**: ``array`` **default**: :ref:`framework.enabled_locales <reference-enabled-locales>`
+
+Restrict the string's characters to those normally used with the associated languages.
+
+For example, the character "π" would be considered suspicious if you restricted the
+locale to "English", because the Greek script is not associated with it.
+
+Passing an empty array, or configuring :ref:`restrictionLevel <restrictionlevel>` to
+``NoSuspiciousCharacters::RESTRICTION_LEVEL_NONE`` will disable this requirement.
+
+``restrictionLevel``
+~~~~~~~~~~~~~~~~~~~~
+
+**type**: ``integer`` **default**: ``NoSuspiciousCharacters::RESTRICTION_LEVEL_MODERATE`` on ICU >= 58, otherwise ``NoSuspiciousCharacters::RESTRICTION_LEVEL_SINGLE_SCRIPT``
+
+Configures the set of acceptable characters for the validated string through a
+specified "level":
+
+* ``NoSuspiciousCharacters::RESTRICTION_LEVEL_MINIMAL`` requires the string's characters to match :ref:`the configured locales <locales>`'.
+* ``NoSuspiciousCharacters::RESTRICTION_LEVEL_MODERATE`` also requires the string to be `covered`_ by Latin and any one other `Recommended`_ or `Limited Use`_ script, except Cyrillic, Greek, and Cherokee.
+* ``NoSuspiciousCharacters::RESTRICTION_LEVEL_HIGH`` (usable with ICU 58 or higher) also requires the string to be `covered`_ by any of the following sets of scripts:
+
+  * Latin + Han + Bopomofo (or equivalently: Latn + Hanb)
+  * Latin + Han + Hiragana + Katakana (or equivalently: Latn + Jpan)
+  * Latin + Han + Hangul (or equivalently: Latn + Kore)
+* ``NoSuspiciousCharacters::RESTRICTION_LEVEL_SINGLE_SCRIPT`` also requires the string to be `single-script`_.
+* ``NoSuspiciousCharacters::RESTRICTION_LEVEL_ASCII`` (usable with ICU 58 or higher) also requires the string's characters to be in the ASCII range.
+
+You can accept all characters by setting this option to
+``NoSuspiciousCharacters::RESTRICTION_LEVEL_NONE``.
+
+.. include:: /reference/constraints/_groups-option.rst.inc
+
+.. include:: /reference/constraints/_payload-option.rst.inc
+
+.. _`Unicode® Technical Standard #39`: https://unicode.org/reports/tr39/
+.. _`cyrillic small letter dze`: https://graphemica.com/%D1%95
+.. _`spoofing attack`: https://en.wikipedia.org/wiki/Spoofing_attack
+.. _`single-script`: https://unicode.org/reports/tr39/#def-single-script
+.. _`covered`: https://unicode.org/reports/tr39/#def-cover
+.. _`Recommended`: https://www.unicode.org/reports/tr31/#Table_Recommended_Scripts
+.. _`Limited Use`: https://www.unicode.org/reports/tr31/#Table_Limited_Use_Scripts

reference/constraints/map.rst.inc

@@ -29,6 +29,7 @@ String Constraints
 * :doc:`UserPassword </reference/constraints/UserPassword>`
 * :doc:`NotCompromisedPassword </reference/constraints/NotCompromisedPassword>`
 * :doc:`CssColor </reference/constraints/CssColor>`
+* :doc:`NoSuspiciousCharacters </reference/constraints/NoSuspiciousCharacters>`
 
 Comparison Constraints
 ~~~~~~~~~~~~~~~~~~~~~~