Issue #1955282 by LewisNyman: Disable Autocapitalize and Autocorrect on user login forms.

core/modules/user/lib/Drupal/user/AccountFormController.php

@@ -40,7 +40,8 @@ public function form(array $form, array &$form_state) {
       '#maxlength' => USERNAME_MAX_LENGTH,
       '#description' => t('Spaces are allowed; punctuation is not allowed except for periods, hyphens, apostrophes, and underscores.'),
       '#required' => TRUE,
-      '#attributes' => array('class' => array('username'), 'autocomplete' => 'off'),
+      '#attributes' => array('class' => array('username'), 'autocorrect' => 'off', 'autocomplete' => 'off', 'autocapitalize' => 'off',
+      'spellcheck' => 'false'),
       '#default_value' => (!$register ? $account->name : ''),
       '#access' => ($register || ($user->uid == $account->uid && user_access('change own username')) || $admin),
       '#weight' => -10,

core/modules/user/user.module

@@ -1225,6 +1225,9 @@ function user_login_form($form, &$form_state) {
     '#description' => t('Enter your @s username.', array('@s' => config('system.site')->get('name'))),
     '#required' => TRUE,
     '#attributes' => array(
+      'autocorrect' => 'off',
+      'autocapitalize' => 'off',
+      'spellcheck' => 'false',
       'autofocus' => 'autofocus',
     ),
   );

core/modules/user/user.pages.inc

@@ -29,6 +29,12 @@ function user_pass() {
     '#size' => 60,
     '#maxlength' => max(USERNAME_MAX_LENGTH, EMAIL_MAX_LENGTH),
     '#required' => TRUE,
+    '#attributes' => array(
+      'autocorrect' => 'off',
+      'autocapitalize' => 'off',
+      'spellcheck' => 'false',
+      'autofocus' => 'autofocus',
+    ),
   );
   // Allow logged in users to request this also.
   if ($user->uid > 0) {