Hello, there are three main ways we differentiate in multitenant situations: self.hq_credentials.aba(this is a unique value for each FI, the FI's staging and Prod environments will have this value set), self.hq_credentials.customer_key(This will be a unique value for each environment i.e. the FI staging and Production environments will be different), self.online_user.user_guid(this is a hash of the user_id and customer key so it will be a unique user id for every user assiociated with Q2).
So depending on which use case you are after depends on which tool you want to use.
If I want a single unique identifier for a given FI, but the FI has multiple routing numbers, then I obviously wouldn't use aba. But customer_key would be constant within a given environment correct? So there would be a separate customer_key for staging vs prod, but in a given env, customer_key will stay the same even if the aba associated with the current user changes - is that correct?