Simple JWT add extra field to payload data in token

I use djoser and rest_framework_simplejwt. This my user model;

class userProfile(models.Model):

    user=models.OneToOneField(User,on_delete=models.CASCADE,related_name="profile")
    date_joined=models.DateTimeField(auto_now_add=True)
    updated_on=models.DateTimeField(auto_now=True)

    def __str__(self):
        return self.user.username

My views.py to get token for users give in below;

class CustomTokenObtainPairView(TokenObtainPairView):

serializer_class = CustomTokenObtainPairSerializer
token_obtain_pair = TokenObtainPairView.as_view()

This is the serializer.py;

class CustomTokenObtainPairSerializer(TokenObtainPairSerializer):
def validate(self, attrs):
    data = super(CustomTokenObtainPairSerializer, self).validate(attrs)
    data.update({'user': self.user.username})
    data.update({'id': self.user.id})
    data.update({'first_name': self.user.first_name})
    data.update({'last_name': self.user.last_name})
    data.update({'is_superuser': self.user.is_superuser})
    return data

I can get access and refresh token like this.

    {
    "refresh": "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ0b2tlbl90eXBlIjoicmVmcmVzaCIsImV4cCI6MTU4ODQxMDY0OCwianRpIjoiNTY2MDhhOGVjYzRiNDZhMmFjYjc0Y2VmMzE2ZGE4YTkiLCJ1c2VyX2lkIjo3fQ.gXk9y3Vq0NlB8ZpU9SFcLWAMplr4_ECTeBg5WTMAuNY",
    "access": "eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJ0b2tlbl90eXBlIjoiYWNjZXNzIiwiZXhwIjoxNTg4NDA5NzQ4LCJqdGkiOiIxM2VlYzQ1MjZkMTQ0ODI4YjgxNjVkZTA0MzlmYjBmMSIsInVzZXJfaWQiOjd9.sQ1G3rur1h3yqj79ZYvzHK1o6mgtHYuzJZlh5OCyg84",
    "user": "x",
    "id": 5,
    "first_name": "x",
    "last_name": "x",
    "is_superuser": false,

}

When encode token using jwt.io payload data is;

{
  "token_type": "access",
  "exp": 1588329561,
  "jti": "944f97343b42448fbaf5461295eb0548",
  "user_id": 5
}

I want to add users first_name, last_name in payload in access token and ı want to get;

    {
          "token_type": "access",
          "exp": 1588329561,
          "jti": "944f97343b42448fbaf5461295eb0548",
          "user_id": 5,
          "user": "x",
          "first_name": "x",
          "last_name": "x",
          "is_superuser": false,
 }

I change my CustomTokenObtainPairSerializer to:

class CustomTokenObtainPairSerializer(TokenObtainPairSerializer):
    @classmethod
    def get_token(cls, user):
        token = super().get_token(user)
        token['first_name'] = user.first_name
        token['last_name'] = user.last_name
        token['username'] = user.username
        token['is_superuser'] = user.is_superuser
        return token