fix placeholder users being resolved by authentication flows

app/Auth/ActiveUserProvider.php

@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Auth;
+
+use Illuminate\Auth\EloquentUserProvider;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Model;
+
+/**
+ * User provider that only resolves non-placeholder users.
+ *
+ * Placeholder users are created by imports and when members are removed from an
+ * organization. They can share an email address with a real user, so resolving a user by
+ * email can return a placeholder instead of the real account. The login flow filters them
+ * out explicitly, but the password broker and the guard credential checks (for example the
+ * password confirmation) resolve users through the configured user provider.
+ *
+ * Registered as the "eloquent" provider driver in the AuthServiceProvider, so it replaces the
+ * built-in one for every provider in config/auth.php.
+ */
+class ActiveUserProvider extends EloquentUserProvider
+{
+    /**
+     * @param  Model|null  $model
+     * @return Builder<Model>
+     */
+    #[\Override]
+    protected function newModelQuery($model = null): Builder
+    {
+        $query = parent::newModelQuery($model);
+        $query->getQuery()->where('is_placeholder', '=', false);
+
+        return $query;
+    }
+}