Webhook Signature Generation/Verification

[timolegros]

Description

In order to ensure end-to-end security for user-facing webhooks, we need to sign all Webhook payloads and then privately provide users with the signing key so they can verify that the request indeed originated from Common.

Tasks

• Generate + store a signing key for all existing Webhooks
• Generate + store a signing key for all new Webhooks
• Update integrations page UI to allow copying the signing key
• Update Knock to enable signing keys for all environments (see docs)
• Update user-facing docs with instructions on how to validate Webhook payload/signatures

Additional context

This is a required change before Eliza Common Client integration can go public.