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: user_authn.go
    path of file: ./repos/Cloudreve/models
    
    the code of the file until where you have to start completion: package model

import (
	"encoding/base64"
	"encoding/binary"
	"encoding/json"
	"fmt"
	"net/url"

	"github.com/cloudreve/Cloudreve/v3/pkg/hashid"
	"github.com/duo-labs/webauthn/webauthn"
)

/*
	`webauthn.User` 接口的实现
*/

// WebAuthnID 返回用户ID
func (user User) WebAuthnID() []byte {
	bs := make([]byte, 8)
	binary.LittleE
    
func (user *User) RemoveAuthn(id string) {
	exists := user.WebAuthnCredentials()
	for i := 0; i < len(exists); i++ {
		idEncoded := base64.StdEncoding.EncodeToString(exists[i].ID)
		if idEncoded == id {
			exists[len(exists)-1], exists[i] = exists[i], exists[len(exists)-1]
			exists = exists[:len(exists)-1]
			break
		}
	}

	res, _ := json.Marshal(exists)
	DB.Model(user).Update("authn", string(res))
}