Extract shared NPM API client

dns_sync/npm_client.py

@@ -125,3 +125,14 @@ class NpmClient:
             )
 
         return data
+
+
+    def certificates(self) -> list[dict[str, Any]]:
+        data = self.get_json("/nginx/certificates")
+
+        if not isinstance(data, list):
+            raise RuntimeError(
+                "NPM certificate response was not a list"
+            )
+
+        return data