Access variable with . in name

Hi,
I am doing integration with Facebook messenger and in the callback URL, Facebook pass parameters with . in name, e.g:
hub.mode
hub.challenge
...
I create a flow with these variables input but in the flow, I could not select them to use.
Please give instruction to get these variables and use it in the flow.
Thanks
Trung.Le

Update: Feedback from Decision
In Decisions we don’t allow the use of “.” In the parameter name(they are used to denote the property of a complex type) and hence the parameters aren’t getting compiled properly.