Is there a simple way to set and get a "global" variable?

You could set it as a global reference in the main.brs or main thread.
For scenegraph --
screen=CreateObject("roSGScreen") 'creates roSGScreen
m.global=screen.getGlobalNode()
m.global.addfield("token","string",FALSE)

Then to set the variable use
m.global.token=value
Where value is the string you want to place into the global space.
And then you can reference it within any component or routine in the app as m.global.token
Or change it again anywhere in the app with m.global.token=value again