Consent-aware storage mechanism

Currently analytics by default stores a field __anon_id into localStorage. However, with GDPR we don't want to store any persistent information until the user gives consent to do so.

We can prevent this by passing in a storage option with a transient storage type (e.g. using @analytics/global-storage-utils).

However, if the user later gives consent, we would want to transition over to using permanent storage.

It would be very helpful if the library was "batteries included" in the sense that it provides an easy way to do this, perhaps with a dedicated consent module.

Initially it could use global storage. But if consent is granted to store tracking cookies, it would copy the relevant data from the global variable storage to localStorage and start using localStorage after that.

It may also be helpful if the library used a different storage options for different kinds of consent.

For example, in Google Tag Manager they have ad_storage, analytics_storage, functionality_storage, personalization_storage, and security_storage that are configured and consented to separately.

I'm not sure if any of the analytics plugins currently would benefit from this distinction but they might.

If the analytics object had 5 different storage objects and each had a flag indicating whether it had consent or not, and plugins could get an event when storage consent changed, they could make use of that to propagate consent state to their upstream library or other make use of this information to adjust their storage related behavior.

Start by reviewing the current storage option and @analytics/global-storage-utils integration described in the issue. Define the consent module’s scope, including transient-to-localStorage migration, separate consent categories, and plugin notifications; the work is done when those behaviors and their integration points are specified and implemented.