How to add middleware to API?

Hello,

I have added the TrimStrings class in my kernel but it has no effects in my API request.

    protected $middleware = [
        \App\Http\Middleware\CheckForMaintenanceMode::class,
        \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,
        \App\Http\Middleware\TrimStrings::class,
        \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,
        \App\Http\Middleware\TrustProxies::class,

    ];

I have just added a blank space in my login username and the blank space is not trimmed in the API side of Laravel.

Any idea why please?

I am on Laravel 5.6

Thank you.