Hi there,
For Apple Health, access is still through HealthKit on the iPhone, which isn’t the same as a pure browser OAuth flow. If you don’t have your own iOS app, Terra offers the Terra Avengers app on the App Store so users can complete the Apple Health connection; your integration still uses the Terra widget / auth APIs on your side, and our docs describe how mobile-only providers interact with redirects and deep links. For Google Fit, you can use the API meaning you won't need to have a mobile app. Your options depend on whether you use the Health & Fitness API path vs on-device Health Connect / SDK, see our integration guides or ask support for the best fit for a web-only product!
https://docs.tryterra.co/health-and-fitness-api/mobile-only-sources