Compat signatures

Outpost can now send a second signature in your previous format alongside the primary one. Receivers keep verifying the old headers and switch to the new scheme on their own schedule.

Use it when you're moving to Outpost from a webhook system you built yourself or from another provider, or when you're changing the signature scheme of a running deployment. Set DESTINATIONS_WEBHOOK_COMPAT_SIGNATURE_HEADER_NAME to enable it, and configure the content template, encoding, algorithm and extra headers with the other DESTINATIONS_WEBHOOK_COMPAT_* variables. Both signatures use the same destination secret, so receivers keep their existing secret. Nothing changes until the header name is set.

The compat signature also works in Standard Webhooks mode. See the change webhook signature scheme guide. It's available now in v1.4.0.