Originally reported here: https://community.developer.atlassian.com/t/forge-fetch-does-not-support-plain-http-only-https/92414

The Forge runtime only supports outbound HTTPS connections. This is documented on the Runtime reference page: https://developer.atlassian.com/platform/forge/function-reference/nodejs-runtime/

If a developer attempts to make a plain HTTP fetch call, the app receives a cryptic HTTP 400 response. Instead, we should detect this situation and return a meaningful error message.