How to encrypt the response from an api?

Personally, I would not attempt this at the luen/php level. This kind of encryption is very well covered by using TLS.

You can do that with a Global Middleware.

You can create a terminable Middleware and declare in the array of global middleware. Inside the method "terminate" you can add the logic to encrypt. Also you have to add another Middleware to decrypt the request.

DecryptRequest

<?php

namespace Illuminate\Session\Middleware;

use Closure;

class DecryptRequest
{
    public function handle($request, Closure $next)
    {
    // Logic to decrypt
        return $next($request);
    }
}

EncryptResponse

<?php

namespace Illuminate\Session\Middleware;

use Closure;

class EncryptResponse
{
    public function handle($request, Closure $next)
    {
        return $next($request);
    }

    public function terminate($request, $response)
    {
        // Logic to encrypt response.
    }
}

Kernel

$app->middleware([
   App\Http\Middleware\DecryptRequest::class,
   App\Http\Middleware\EncryptResponse::class
]);

Thank you agCepeda for suggesting middleware way of doing it, but what I want is how to encrypt the response of my api? Is it good practice to encrypt my response using Encrypt class the lumen/laravel provides? Or is there any other approach for this, can you suggest something on this?

Laravel use blowfish to encrypt. This algorithm has not reverse. You must use and algorithm that allows decrypt also.

You can use RSA algorithm it is used to transfer data. You can use a paragonie/easyrsa package or another package that fits in your app.