Set Hapi plugin option to value from async function call in Node.js

I have a Hapi web application running on Node.js that requires a plugin to handle session using yar. This all works OK except that I need to call an async function the get the cookie password from an Azure Key Vault. I can't see a way to call an async function in this scenario. A cut down version of my index.js looks like this:

async function createServer () {
  const server = hapi.server({
    port: config.port,
    cache: [{
      name: 'session',
      provider: {
        constructor: catbox,
        options: cacheConfig.catboxOptions
      }
    }],
  })

  await server.register(require('./plugins/yar'))

  return server
}

module.exports = createServer

And the yar.js file looks like this:

module.exports = {
  plugin: require('@hapi/yar'),
  options: {
    maxCookieSize: 0,
    storeBlank: true,
    cache: {
      cache: 'session',
      expiresIn: cacheConfig.expiresIn
    },
    cookieOptions: {
      password: (await readSecret('COOKIE-PASSWORD').value),//This line fails
      isSecure: config.cookieOptions.isSecure,
      ttl: cacheConfig.expiresIn
    }    
  }
}

The call to readSecret is the one that is causing me issues as readSecret returns a Promise. How can I fix this ideally without changing the index.js file?

Well I think I've found a solution although I'm not sure it's the best way of doing it. I've created a plugin to register the yar plugin.

This is my code that is now in the yar.js file:

module.exports = {
  name: 'yar',
  register: async function (server, options) {

    const cookiePassword = (await readSecret('COOKIE-PASSWORD')).value

    server.register({
      plugin: require('@hapi/yar'),

      options: {
        maxCookieSize: 0,
        storeBlank: true,
        cache: {
          cache: 'session',
          expiresIn: cacheConfig.expiresIn
        },
        cookieOptions: {
          password: cookiePassword,
          isSecure: config.cookieOptions.isSecure,
          ttl: cacheConfig.expiresIn
        }
      }
    })
  },
}