You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: token.go
    path of file: ./repos/ziti/controller/oidc_auth
    
    the code of the file until where you have to start completion: package oidc_auth

import (
	"encoding/json"
	"fmt"
	"github.com/golang-jwt/jwt/v5"
	"github.com/zitadel/oidc/v2/pkg/oidc"
	"time"
)

const (
	ClaimAudienceOpenZiti = "openziti"

	CustomClaimApiSessionId      = "z_asid"
	CustomClaimExternalId        = "z_eid"
	CustomClaimIsAdmin           = "z_ia"
	CustomClaimsConfigTypes      = "z_ct"
	CustomClaimsCertFingerprints = "z_cfs"

	DefaultAccessToken
    
func (c *RefreshClaims) MarshalJSON() ([]byte, error) {
	var customBuf, idBuf []byte
	var err error

	if idBuf, err = json.Marshal(c.IDTokenClaims); err != nil {
		return nil, fmt.Errorf("refresh token oidc claims marhsalling error: %w", err)
	}

	if customBuf, err = json.Marshal(c.CustomClaims); err != nil {
		return nil, fmt.Errorf("refresh token custom claims marhsalling error: %w", err)
	}

	mergeMap := map[string]any{}

	_ = json.Unmarshal(idBuf, &mergeMap)
	_ = json.Unmarshal(customBuf, &mergeMap)

	return json.Marshal(mergeMap)
}