How can I encode in base64 my instance ID

I need to encode my faunadb instance's id because I use it in an URL of this type /mission/(id number)/team

I create instance with this:

/* code from functions/todos-create.js */
import faunadb from 'faunadb' /* Import faunaDB sdk */
/* configure faunaDB Client with our secret */
const q = faunadb.query
const client = new faunadb.Client({
  secret: process.env.FAUNADB_SECRET
})

/* export our lambda function as named "handler" export */
exports.handler = (event, context, callback) => {
  /* parse the string body into a useable JS object */


  const eventBody = JSON.stringify(event.body)
  const data = JSON.parse(eventBody)
  const mission = {
    data: JSON.parse(data)
  }
  // {"title":"What I had for breakfast ..","completed":true}
  /* construct the fauna query */
  return client.query(q.Create(q.Ref("classes/missions"), mission))
  .then((response) => {
    console.log("success", response)
    /* Success! return the response with statusCode 200 */
    return callback(null, {
      statusCode: 200,
      body: JSON.stringify(response)
    })
  }).catch((error) => {
    console.log("error", error)
    /* Error! return the error with statusCode 400 */
    return callback(null, {
      statusCode: 400,
      body: JSON.stringify(error)
    })
  })
}

I call this lambda with a function in a service:

  createMission(data) {
    return fetch('/.netlify/functions/mission-create', {
      body: JSON.stringify(data),
      method: 'POST'
    }).then(response => {
      return response.json();
    });
  }

and then I load this at the init of my page with adress '/mission/(id number)/team' :

this._missionService.readById(this.route.snapshot.params.missionId)

with this lambda by a service again:

import faunadb from 'faunadb'

const q = faunadb.query
const client = new faunadb.Client({
  secret: process.env.FAUNADB_SECRET
})

exports.handler = (event, context, callback) => {
  const id = event.path.match(/([^\/]*)\/*$/)[0];
  console.log(`Function 'mission-read' invoked. Read id: ${id}`)
  return client.query(q.Get(q.Ref(q.Class("missions"), id)))
  .then((response) => {
    console.log("success", response)
    return callback(null, {
      statusCode: 200,
      body: JSON.stringify(response)
    })
  }).catch((error) => {
    console.log("error", error)
    return callback(null, {
      statusCode: 400,
      body: JSON.stringify(error)
    })
  })
}

Actually this is not secure because url handling with id number is possible to access all my missions. I want to encode in base64 this id, but I don't know how to do this, I begin in dev and I thought first encrypt id in service and decrypt it in service but someone said me front is not secure, then I want to use base64 in back. Thanks for advice !