You can’t. Homey’s OAuth2 login view always opens the URL inside Homey’s own in-app browser, and the SDK doesn’t provide any way to force it to open in the device’s external browser.
The whole OAuth flow is handled internally by the Homey app. The SDK only gives you the callback and the URL — how that URL is opened is completely controlled by the Homey mobile app, not by your code.
Because of this, Google’s restriction against embedded webviews can’t be avoided. The only real option is to ask Athom to add external-browser support for OAuth login in a future update.

You should already know this you dumb stupid fuck. Welcome to Stackoverflow! We krazy in this bitch