fix(ssh): verify the host key netOrk expects, report the one seen (NetOrk/netork#1167)

The driver accepted any SSH host key. It now verifies through
napalm-device-types' HostKeyCheck (>= 4.19.0): with a known key in
optional_args["ssh_host_keys"] any other key is refused before login, and
every key seen is reported to optional_args["ssh_host_key_observer"].
Without either argument it connects as before (first use).

napalm_netgear/netgear_smart.py

@@ -46,6 +46,7 @@ from napalm.base.exceptions import (
     ReplaceConfigException,
 )
 from napalm.base.netmiko_helpers import netmiko_args
+from napalm_device_types.ssh_host_keys import HostKeyCheck, SshHostKeyMismatch
 import napalm.base.constants as C
 
 
@@ -126,6 +127,8 @@ class NetgearSmartDriver(ConfigLifecycleMixin, SnmpAgentMixin, SwitchDriver):
         optional_args.setdefault("banner_timeout", 20)
 
         self.netmiko_optional_args = netmiko_args(optional_args)
+        # The host key to expect, and where the one seen is reported (netork#1167).
+        self._host_key = HostKeyCheck(optional_args, hostname, self.port)
 
         # Config management state
         self._candidate_config: Optional[str] = None
@@ -146,16 +149,20 @@ class NetgearSmartDriver(ConfigLifecycleMixin, SnmpAgentMixin, SwitchDriver):
     def open(self) -> None:
         """Open an SSH connection to the device."""
         try:
-            self.device = ConnectHandler(
-                device_type=self.NETMIKO_DEVICE_TYPE,
-                host=self.hostname,
-                username=self.username,
-                password=self.password,
-                timeout=self.timeout,
-                **self.netmiko_optional_args,
-            )
+            with self._host_key.netmiko(self.netmiko_optional_args) as netmiko_kwargs:
+                self.device = ConnectHandler(
+                    device_type=self.NETMIKO_DEVICE_TYPE,
+                    host=self.hostname,
+                    username=self.username,
+                    password=self.password,
+                    timeout=self.timeout,
+                    **netmiko_kwargs,
+                )
+            self._host_key.observe(self.device.remote_conn_pre.get_transport())
             if not self.force_no_enable:
                 self.device.enable()
+        except SshHostKeyMismatch:
+            raise  # refused before the login; nothing was sent
         except NetmikoTimeoutException as exc:
             raise ConnectionException(f"Cannot connect to {self.hostname}: {exc}") from exc
         except NetmikoAuthenticationException as exc: