pylxd/client: guard against cert=None

doc/source/authentication.rst

@@ -31,7 +31,7 @@ essentially meaning that the authentication has not yet occurred.
 
     >>> from pylxd import Client
     >>> client = Client(
-    ...     endpoint='http://10.0.0.1:8443',
+    ...     endpoint='https://10.0.0.1:8443',
     ...     cert=('lxd.crt', 'lxd.key'))
     >>> client.trusted
     False

doc/source/usage.rst

@@ -24,7 +24,7 @@ certificate to the `verify` argument:
 
     >>> from pylxd import Client
     >>> client = Client(
-    ...     endpoint='http://10.0.0.1:8443',
+    ...     endpoint='https://10.0.0.1:8443',
     ...     cert=('/path/to/client.crt', '/path/to/client.key'),
     ...     verify='/path/to/server.crt')
 
@@ -38,7 +38,7 @@ for TLS verification.
 
     >>> from pylxd import Client
     >>> client = Client(
-    ...     endpoint='http://10.0.0.1:8443',
+    ...     endpoint='https://10.0.0.1:8443',
     ...     cert=('/path/to/client.crt', '/path/to/client.key'),
     ...     verify=False)
 

pylxd/client.py

@@ -570,7 +570,15 @@ def assert_has_api_extension(self, name):
     def authenticate(self, secret, use_token_auth=True):
         if self.trusted:
             return
-        cert = open(self.api.session.cert[0]).read().encode("utf-8")
+
+        if not isinstance(self.api.session.cert, tuple):
+            raise exceptions.ClientConnectionFailed("No client certificate specified")
+
+        try:
+            with open(self.api.session.cert[0]) as f:
+                cert = f.read().encode("utf-8")
+        except FileNotFoundError:
+            raise exceptions.ClientConnectionFailed("Client certificate not found")
 
         # Quirk to handle 5.21 that supports explicit trust tokens as well as
         # password auth. We need to ascertain if the provided secret is indeed a