Replace emarref/jwt with lcobucci/jwt

Refactor all JWT-related components
Replace RS256 with ES256 as a preferred JWT algorithm

api/controllers/SignupController.php

@@ -89,7 +89,7 @@ class SignupController extends Controller {
 
         return array_merge([
             'success' => true,
-        ], $result->getAsResponse());
+        ], $result->formatAsOAuth2Response());
     }
 
 }