add name sanitization

README.md

@@ -52,6 +52,11 @@ login by attacking via ssh or another mean.
 To change your password, you should login in your jupyterhub account, 
 go to `<your_server_ip>/hub/auth/change-password` and change the password. 
 
+#### I'm getting an error when creating my username
+
+Usernames cannot contain spaces or commas. Please check if your username is free 
+of these characters. 
+
 ## Security
 
 When using `FirstUseAuthenticator` it is advised to automatically prepend the

firstuseauthenticator/firstuseauthenticator.py

@@ -93,6 +93,12 @@ class FirstUseAuthenticator(Authenticator):
         """
         return self.db.query(User).filter_by(name=username).first() is not None
 
+    def validate_username(self, name):
+        invalid_chars = [',', ' ']
+        if any((char in name) for char in invalid_chars):
+            return False
+        return super().validate_username()
+
     @gen.coroutine
     def authenticate(self, handler, data):
         username = data['username']