GTM consent mode

[maureenlholland]

One-line summary

GTM implementation of Google consent mode: https://developers.google.com/tag-platform/security/guides/consent?consentmode=advanced#tag-manager_2

Denial is default. Updates only run with user-driven consent pref (set by marketing opt-out checkbox, consent banner or cookie page)

on /landing/get, we allow analytics by default

Significant changes and points to review

Issue / Bugzilla link

https://mozilla-hub.atlassian.net/browse/WT-602

Testing

• GTM is loaded according to usual gates (respecting DNT/GPC, consent-required, analytics cookie)

When GTM is loaded on most pages:

• and there is no existing analytics cookie, defaults are denied
• and there is an existing analytics cookie TRUE, defaults are granted

When GTM is loaded on /landing/get

• and there is no existing analytics cookie, analytics default is granted, ad defaults are denied

When user indicates pref, an 'update' dataLayer event appears:

• after clicking marketing opt out checkbox on /landing/get
• after clicking ACCEPT on consent banner on /landing/get (when a consent required geo, ie. http://localhost:8000/en-US/landing/get/?geo=FR)
• after setting cookie pref: http://localhost:8000/en-US/privacy/websites/cookie-settings/

Google verification docs: https://developers.google.com/tag-platform/security/guides/consent-debugging#start-debugging

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.56%. Comparing base (b9940cf) to head (6e88cec).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #955      +/-   ##
==========================================
- Coverage   81.42%   78.56%   -2.87%     
==========================================
  Files         119      121       +2     
  Lines        6574     6881     +307     
==========================================
+ Hits         5353     5406      +53     
- Misses       1221     1475     +254     

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