Keep Unauthenticated Server-Side Request Forgery via POST /providers/healthcheck

Keep (commit 91c75e0) contains a server-side request forgery vulnerability that allows unauthenticated attackers to make the backend issue arbitrary HTTP requests by supplying attacker-controlled host values to the unprotected healthcheck endpoint. Attackers can send a crafted JSON payload with a malicious host parameter to cause the backend to issue outbound requests to internal services or cloud metadata endpoints, enabling theft of cloud credentials and internal network reconnaissance.

The keep for python, as distributed on PyPI, included a code-execution backdoor inserted by a third party. The current version, without this backdoor, is 1.2.