It's common to want to first fetch secrets from a third-party location, or perform some other action before returning your Payload config. You could always do this using a pattern like this:

const fetchAndBuildConfig = async () => {
  const mySecrets = await fetchSecrets()
  
  return buildConfig({
    secret: mySecrets.PAYLOAD_SECRET,
    // etc
  })
}

export default fetchAndBuildConfig()

But this is more verbose than it needs to be. We could simplify and handle that complexity just by allowing the developer to pass an async function to buildConfig itself, like this:

export default buildConfig(async () => {
  const mySecrets = await fetchSecrets()
  
  return {
    secret: mySecrets.PAYLOAD_SECRET,
    // etc
  }
})

This PR makes this simpler pattern possible.