Support for the logout route and for the OAuth error validation

src/examples/app.py

@@ -129,9 +129,19 @@ def spreadsheet(self, id):
         )
         return contents
 
+    @appier.route("/logout", "GET")
+    def logout(self):
+        return self.oauth_error(None)
+
     @appier.route("/oauth", "GET")
     def oauth(self):
         code = self.field("code")
+        error = self.field("error")
+        appier.verify(
+            not error,
+            message = "Invalid OAuth response (%s)" % error,
+            exception = appier.OperationalError
+        )
         api = self.get_api()
         access_token = api.oauth_access(code)
         self.session["gg.access_token"] = access_token