callbacks service draft

api/edge/callbacks/entrypoint.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+set -eu
+
+if [ -n "${VAULT_TOKEN_FILE:-}" ] && [ -f "${VAULT_TOKEN_FILE}" ]; then
+  token="$(cat "${VAULT_TOKEN_FILE}" 2>/dev/null | tr -d '[:space:]')"
+  if [ -n "${token}" ]; then
+    export VAULT_TOKEN="${token}"
+  fi
+fi
+
+if [ -z "${VAULT_TOKEN:-}" ]; then
+  echo "[entrypoint] VAULT_TOKEN is not set; expected Vault Agent sink to write a token to ${VAULT_TOKEN_FILE:-/run/vault/token}" >&2
+fi
+
+exec "$@"