Make login case insensitive for PostgreSQL in Laravel Framework

AuthServiceProvider.php

<?php

namespace App\Providers;

use App\Policies\UserPolicy;
use App\Support\Auth\EloquentUserProvider;
use App\User;
use Illuminate\Foundation\Support\Providers\AuthServiceProvider as ServiceProvider;
use Illuminate\Support\Facades\Auth;

class AuthServiceProvider extends ServiceProvider
{
    /**
     * The policy mappings for the application.
     *
     * @var array
     */
    protected $policies = [
        User::class => UserPolicy::class,
    ];

    /**
     * Register any authentication / authorization services.
     *
     * @return void
     */
    public function boot()
    {
        $this->registerPolicies();

        Auth::provider('eloquent', function ($app, $config) {
            return new EloquentUserProvider($app['hash'], $config['model']);
        });
    }
}

EloquentUserProvider.php

<?php

namespace App\Support\Auth;

use Illuminate\Auth\EloquentUserProvider as UserProvider;
use Illuminate\Contracts\Support\Arrayable;
use Illuminate\Database\Eloquent\Builder;
use Illuminate\Database\Query\Grammars\PostgresGrammar;
use Illuminate\Support\Str;

class EloquentUserProvider extends UserProvider
{
    /**
     * Retrieve a user by the given credentials.
     *
     * @param array $credentials
     *
     * @return Builder|\Illuminate\Database\Eloquent\Model|object|void
     */
    public function retrieveByCredentials(array $credentials)
    {
        if (empty($credentials) ||
            (count($credentials) === 1 &&
                array_key_exists('password', $credentials))) {
            return;
        }

        // First we will add each credential element to the query as a where clause.
        // Then we can execute the query and, if we found a user, return it in a
        // Eloquent User "model" that will be utilized by the Guard instances.
        $query = $this->newModelQuery();

        foreach ($credentials as $key => $value) {
            if (Str::contains($key, 'password')) {
                continue;
            }

            if ($this->isPostgresGrammar($query) && in_array($key, ['email', 'username'])) {
                $query->whereRaw("LOWER({$key}) = LOWER(:value)", ['value' => $value]);
            } elseif (is_array($value) || $value instanceof Arrayable) {
                $query->whereIn($key, $value);
            } else {
                $query->where($key, $value);
            }
        }

        return $query->first();
    }

    protected function isPostgresGrammar(Builder $query)
    {
        return $query->getQuery()->getGrammar() instanceof PostgresGrammar;
    }
}