@daniel-zahariev
Why do you want to do that? The required params here should be coming from Shopify through URL params anyhow.

@tareqtms because i'm building an API for Shopify embedded app and i want to use the Referrer HTTP header and verify that it has valid URL params (they should be sent from Shopify). And in order to do that i want to pass the extracted params to the verification method.

@daniel-zahariev
Everything sent from Shopify are already available under $_GET variable. What extra you want to add there?
However, if you want you can add your extra parameters to the $_GET variable itself.

The API i'm building is called via JavaScript fetch method and so i want to use the HTTP Referrer header to do the authorisation. Don't think it's the best way to play with $_GET variable.