Extending the default EloquentUserProvider (Laravel 9)

auth.php

<?php

return [
    /* ... */

   /*
    |--------------------------------------------------------------------------
    | User Providers
    |--------------------------------------------------------------------------
    |
    | All authentication drivers have a user provider. This defines how the
    | users are actually retrieved out of your database or other storage
    | mechanisms used by this application to persist your user's data.
    |
    | If you have multiple user tables or models you may configure multiple
    | sources which represent each model / table. These sources may then
    | be assigned to any extra authentication guards you have defined.
    |
    | Supported: "database", "eloquent"
    |
    */
    'providers' => [
        'users' => [
            'driver' => 'custom',
            'model' => App\Models\User::class,
        ],
    ],

    /* ... */
];

AuthServiceProvider.php

<?php

namespace App\Providers;

use App\Auth\UserProvider;
use Illuminate\Foundation\Support\Providers\AuthServiceProvider as ServiceProvider;

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

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

        $this->app->auth->provider('custom', function ($app, array $config) {
            return new UserProvider($app['hash'], $config['model']);
        });
    }
}

EloquentUserProvider.php

<?php

namespace App\Providers\Auth;

use Closure;
use Illuminate\Contracts\Auth\Authenticatable as UserContract;
use Illuminate\Contracts\Auth\UserProvider;
use Illuminate\Contracts\Hashing\Hasher as HasherContract;
use Illuminate\Contracts\Support\Arrayable;
use Illuminate\Support\Str;
use Illuminate\Auth\EloquentUserProvider as BaseEloquentUserProvider;

class EloquentUserProvider extends BaseEloquentUserProvider
{
    /**
     * Retrieve a user by the given credentials.
     *
     * @param  array  $credentials
     * @return \Illuminate\Contracts\Auth\Authenticatable|null
     */
    public function retrieveByCredentials(array $credentials)
    {
        if (
            empty($credentials) ||
            (count($credentials) === 1 &&
                Str::contains($this->firstCredentialKey($credentials), 'password'))
        ) {
            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 (is_array($value) || $value instanceof Arrayable) {
                $query->whereIn($key, $value);
            } elseif ($value instanceof Closure) {
                $value($query);
            } else {
                $query->where($key, $value);
            }
        }

        return $query->first();
    }
}

I use this to encrypt user emails.

php artisan make:migration add_email_key_to_users

// ...
    public function up()
    {
        Schema::table('users', function (Blueprint $table) {
            $table->text('email')->unique(false)->change();
            $table->string('email_key')->unique()->after('email');
        });
    }
    public function down()
    {
        Schema::table('users', function (Blueprint $table) {
            $table->string('email')->unique()->change();
            $table->dropUnique(['email_key']);
            $table->dropColumn('email_key');
        });
    }
// ...

app/Models/User.php

    protected $casts = [
        // ...
        'email' => 'encrypted',
    ];

    public static function boot()
    {
        parent::boot();
        self::creating(function ($user) {
            if (!$user->email_key) {
                $user->email_key = substr(md5($user->email), 0, 255);
            }
        });
    }

app/Providers/Auth/EloquentUserProvider.php:40

            // ...
            if (Str::contains($key, 'password')) {
                continue;
            }

            ## BEGIN EDIT - convert email to email_key
            if (Str::contains($key, 'email')) {
                $key = 'email_key';
                $value = substr(md5($value), 0, 255);
            }
            ## END EDIT ##

            if (is_array($value) || $value instanceof Arrayable) {
            // ...