OAUTHv2 client and secret can be specified in the configuration of the
agent or globally using ENV['FITBIT_OAUTH2_CLIENT'] and
ENV['FITBIT_OAUTH2_SECRET'].
The agent will remember some (loopback=50) activities so it can update
them instead of creating new ones.
Refer to this page for a list of properties of the events created.
After the agent is created go into its description to complete the OAUTHv2 flow and authorize it to read your Fitbit data.