Global setup for Authentication

[GestiSam]

We use the same appId and secret for all our customers, would be nice to be able to enter the credentials globally in the setup instead of in each specific tenant.

[Freddy-D4P]

@ajkauffmann is refactoring this piece due to problems with using the same ClientId and ClienSecret, see issue #40 - maybe he can take this into account as well?