Feature/16969 emails and idn

src/config/GeneralConfig.php

@@ -3212,6 +3212,31 @@ class GeneralConfig extends BaseConfig
      */
     public bool $useEmailAsUsername = false;
 
+    /**
+     * @var bool Whether [nontransitional processing](https://www.php.net/manual/en/intl.constants.php#constant.idna-nontransitional-to-unicode) should be used when using [idn_to_utf8()](https://www.php.net/manual/en/function.idn-to-utf8.php).
+     *
+     * When your system supports IDNA ASCII strings, the domain name is converted from IDNA ASCII to Unicode using INTL_IDNA_VARIANT_UTS46 by default.
+     * INTL_IDNA_VARIANT_UTS46 uses UTS 46 algorithm which is consistent with the requirements of the IDNA2008 protocol and mostly compatible with IDNA2003 (which was deprecated in php 7.2.0).
+     *
+     * There are a handful of characters which result in different resolution of IDNs between IDNA2008 and IDNA2003, unless explicit action is taken.
+     * Those characters are: German eszett, Greek final sigma, joiner characters (ZWJ and ZWNJ). [More info](https://unicode.org/reports/tr46/#Deviations))
+     *
+     * For example, by default, `ß` will be translated to `ss` by the `idn_to_utf8` method. If you'd like to preseve it as `ß`, you need to set the `useIdnaNontransitionalToUnicode` to `true`.
+     *
+     * ::: code
+     * ```php Static Config
+     * ->useIdnaNontransitionalToUnicode(true)
+     * ```
+     * ```shell Environment Override
+     * CRAFT_USE_IDNA_NONTRANSITIONAL_TO_UNICODE=true
+     * ```
+     * :::
+     *
+     * @group System
+     * @since 5.9.0
+     */
+    public bool $useIdnaNontransitionalToUnicode = false;
+
     /**
      * @var bool Whether [iFrame Resizer options](http://davidjbradshaw.github.io/iframe-resizer/#options) should be used for Live Preview.
      *
@@ -6962,6 +6987,33 @@ public function useEmailAsUsername(bool $value = true): self
         return $this;
     }
 
+    /**
+     * Whether [nontransitional processing](https://www.php.net/manual/en/intl.constants.php#constant.idna-nontransitional-to-unicode) should be used when using [idn_to_utf8()](https://www.php.net/manual/en/function.idn-to-utf8.php).
+     *
+     * When your system supports IDNA ASCII strings, the domain name is converted from IDNA ASCII to Unicode using INTL_IDNA_VARIANT_UTS46 by default.
+     * INTL_IDNA_VARIANT_UTS46 uses UTS 46 algorithm which is consistent with the requirements of the IDNA2008 protocol and mostly compatible with IDNA2003 (which was deprecated in php 7.2.0).
+     *
+     * There are a handful of characters which result in different resolution of IDNs between IDNA2008 and IDNA2003, unless explicit action is taken.
+     * Those characters are: German eszett, Greek final sigma, joiner characters (ZWJ and ZWNJ). [More info](https://unicode.org/reports/tr46/#Deviations))
+     *
+     * For example, by default, `ß` will be translated to `ss` by the `idn_to_utf8` method. If you'd like to preseve it as `ß`, you need to set the `useIdnaNontransitionalToUnicode` to `true`.
+     *
+     * ```php
+     * ->useIdnaNontransitionalToUnicode(true)
+     * ```
+     *
+     * @group System
+     * @param bool $value
+     * @return self
+     * @see $useIdnaNontransitionalToUnicode
+     * @since 5.9.0
+     */
+    public function useIdnaNontransitionalToUnicode(bool $value = false): self
+    {
+        $this->useIdnaNontransitionalToUnicode = $value;
+        return $this;
+    }
+
     /**
      * Whether [iFrame Resizer options](http://davidjbradshaw.github.io/iframe-resizer/#options) should be used for Live Preview.
      *

src/elements/User.php

@@ -993,7 +993,7 @@ protected function defineRules(): array
         $rules[] = [['lastLoginDate', 'lastInvalidLoginDate', 'lockoutDate', 'lastPasswordChangeDate', 'verificationCodeIssuedDate'], DateTimeValidator::class];
         $rules[] = [['invalidLoginCount', 'photoId', 'affiliatedSiteId'], 'number', 'integerOnly' => true];
         $rules[] = [['username', 'email', 'unverifiedEmail', 'fullName', 'firstName', 'lastName'], 'trim', 'skipOnEmpty' => true];
-        $rules[] = [['email', 'unverifiedEmail'], 'email', 'enableIDN' => App::supportsIdn(), 'enableLocalIDN' => false];
+        $rules[] = [['email', 'unverifiedEmail'], 'email', 'enableIDN' => App::supportsIdn(), 'enableLocalIDN' => App::supportsIdn()];
         $rules[] = [['email', 'username', 'fullName', 'firstName', 'lastName', 'password', 'unverifiedEmail'], 'string', 'max' => 255];
         $rules[] = [['verificationCode'], 'string', 'max' => 100];
         $rules[] = [['email'], 'required', 'when' => fn() => !$this->getIsDraft()];

src/fields/Email.php

@@ -145,7 +145,7 @@ public function getElementValidationRules(): array
     {
         return [
             ['trim'],
-            ['email', 'enableIDN' => App::supportsIdn(), 'enableLocalIDN' => false],
+            ['email', 'enableIDN' => App::supportsIdn(), 'enableLocalIDN' => App::supportsIdn()],
         ];
     }
 

src/helpers/StringHelper.php

@@ -1949,9 +1949,14 @@ public static function idnToUtf8Email(string $email): string
             return $email;
         }
 
+        if (Craft::$app->getConfig()->getGeneral()->useIdnaNontransitionalToUnicode && defined('IDNA_NONTRANSITIONAL_TO_UNICODE')) {
+            $variant = IDNA_NONTRANSITIONAL_TO_UNICODE;
+        } else {
+            $variant = INTL_IDNA_VARIANT_UTS46;
+        }
         $parts = explode('@', $email, 2);
         foreach ($parts as &$part) {
-            if (($part = idn_to_utf8($part, IDNA_DEFAULT, INTL_IDNA_VARIANT_UTS46)) === false) {
+            if (($part = idn_to_utf8($part, IDNA_DEFAULT, $variant)) === false) {
                 return $email;
             }
         }