"Code" field is needed for a backend server

[pipoa]

For backend server used, "code" field is very important. Reference to Line API document https://developers.line.biz/en/docs/line-login/web/integrate-line-login/#receiving-the-authorization-code

Is there a way to get this field in login function? Recently, we need to get email scope from back end side, because front end is not trustable. Email can be forged even though access_token is correct from front end. With a fake email, one can take over any account he wants.