The Microsoft nodejs example code for a Microsoft Teams outgoing webhook handler in Javascript from https://github.com/OfficeDev/msteams-samples-outgoing-webhook-nodejs modifed for a Cloudflare Worker. index.js is the content of the Workers script.
For dev, set SECRET_TOKEN in wrangler.toml. In production, recommended to use Secrets
See https://docs.microsoft.com/en-us/microsoftteams/platform/webhooks-and-connectors/how-to/add-outgoing-webhook for adding an outgoing webhook, and details on the HMAC signature in the request.
To generate using wrangler
wrangler generate projectname https://github.com/piersc/msteams-outgoing-webhook-bot-worker
To deploy using serverless add a serverless.yml file.