@@ -40,9 +40,13 @@ async def _get(endpoint):

     return resp

-def _normalize_hostname(hostname):

-    if not hostname.endswith('nordvpn.com'):

-        return f'{hostname}.nordvpn.com'

+def normalized_hostname(hostname):

+    """Return the fully qualified domain name of a NordVPN host."""

+    host, *domain = hostname.split('.')

+    if not domain:

+        return f'{host}.nordvpn.com'

+    elif tuple(domain) != ('nordvpn', 'com'):

+        raise ValueError(f'invalid NordVPN host {hostname}')

     return hostname

@@ -68,7 +72,7 @@ async def host_config(host, protocol='tcp'):

         the trailing '.nordvpn.com'.

     protocol: str, 'tcp' or 'udp'

     """

-    host = _normalize_hostname(host)

+    host = normalized_hostname(host)

     resp = await _get(f'files/download/{_config_filename(host, protocol)}')

     return await resp.text()

@@ -90,7 +94,7 @@ async def host_load(host=None):

         to percentage load.

     """

     if host:

-        host = _normalize_hostname(host)

+        host = normalized_hostname(host)

     endpoint = f'server/stats/{host}' if host else 'server/stats'

     resp = await _get(endpoint)

     resp = await resp.json()

@@ -128,3 +132,17 @@ async def dns_servers():

     """Return a list of ip addresses of NordVPN DNS servers."""

     resp = await _get('dns/smart')

     return await resp.json()

+

+

+async def valid_credentials(username, password):

+    """Return True if NordVPN accepts the username/password combination.

+

+    Sometimes connecting to the VPN server gives an authentication error even

+    if the correct credentials are given. This function is useful to first verify

+    credentials so as to avoid unecessary reconnection attempts.

+

+    Parameters

+    ----------

+    username, password : str

+    """

+    return True