令牌签名后 JWT 声明不保留

package main

import (
    "fmt"
    "time"

    "github.com/golang-jwt/jwt/v4"
)

type mycustomclaims struct {
    userid int
    jwt.registeredclaims
}

func (app *config) generatejwt(userid int) {

    //code to generate jwt
    jt := jwt.newwithclaims(jwt.signingmethodhs256, mycustomclaims{
        userid,
        jwt.registeredclaims{
            expiresat: jwt.newnumericdate(time.now().add(3 * time.hour)),
            issuedat:  jwt.newnumericdate(time.now()),
        },
    })

    fmt.println("what was put", jt.claims.(mycustomclaims).userid)
    token, _ := jt.signedstring(app.secret)

    //code to check whether claims are retained
    parsed_token, _ := jwt.parsewithclaims(token, &mycustomclaims{}, func(t *jwt.token) (interface{}, error) {
        return app.secret, nil
    })

    fmt.println("what was parsed", parsed_token.claims.(*mycustomclaims).userid)

}

What was put 8
What was parsed 0

type MyCustomClaims struct {
    UserID int `json:"userid"`
    jwt.RegisteredClaims
}