install phpseclib and create function to sign every body request

composer.json

@@ -16,5 +16,7 @@
             "email": "me@bacarin.dev"
         }
     ],
-    "require": {}
+    "require": {
+        "phpseclib/phpseclib": "~3.0"
+    }
 }

src/Kore.php

@@ -2,17 +2,19 @@
 
 namespace Kontrl\PhpKore;
 
+use phpseclib3\Crypt\PublicKeyLoader;
+
 class Kore
 {
     private $url = 'https://httpbin.org';
-    private $token;
 
     public function __construct(){
-        $this->token = $this->auth();
+        
     }
 
-    public function auth(){
-        return '';
+    public function signBody(array $body, string|array $key, string|bool $password = false){
+        $publicKey = PublicKeyLoader::loadPrivateKey($key, $password);
+        return base64_encode($publicKey->sign(json_encode($body)));
     }
     
     public function testRequest(){