Smartsheet Webhook Callbacks with API Gateway

I recently had a need to auto-populate the values of drop-down list columns in Smartsheet based on a list of values in a “lookup” sheet (this is similar to using named ranges to provide drop-down values in Excel). While there isn’t a way to do this with native Smartsheet features, it’s rather simple to implement via Smartsheet’s API and webhooks. Webhooks require a publicly-accessible callback URL, which can be a bit of a pain if you don’t happen to have a server available to host the callback.