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Fixes: MetaMask/MetaMask-planning#7148
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Support webcredential for ios google login
Part 3/4 - Support legacy/ webcredential ios google login based on
feature flag

This pr add feature flag for the ios google login
use legacy ios google login when flag is true
use webcredential ios google login when flag is false for ios > 17.4

Part 1/ 4 - #27741
Part 2/ 4 - #27848
Part 3/ 4 - #27850 (defer to 7.72.0)
Part 4/ 4 -
[#27875](#27875)

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CHANGELOG entry: Support legacy/ webcredential ios google login based
feature flag

Fixes:

```gherkin
Feature: iOS Google OAuth and token refresh (seedless)

  Scenario: Sign in with Google on iOS using legacy configuration
    Given the legacy iOS Google feature flag and OS version yield legacy client/redirect
    When the user completes seedless Google onboarding
    Then login completes and the app persists onboarding OAuth context as expected

  Scenario: Sign in with Google on iOS using web client and universal link redirect
    Given the app selects the web Google client and universal link redirect for iOS Google
    When the user completes Google OAuth via the browser/universal link flow
    Then the user returns to the app with a successful login

  Scenario: Refresh auth tokens after Google login on iOS
    Given an existing seedless Google session on iOS
    When the client refreshes JWT / auth tokens (e.g. after background or controller refresh)
    Then refresh succeeds without client_id mismatch errors

  Scenario: Wallet reset clears seedless onboarding state
    Given seedless onboarding metadata exists in Redux
    When the user deletes the wallet or resets onboarding as implemented
    Then seedless onboarding state is cleared with other onboarding fields
```

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- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [ ] I've documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I've applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Medium Risk**
> Changes OAuth login/refresh behavior and auth-connection selection for
iOS Google, including new Redux-persisted client IDs and feature-flagged
config switching; mistakes could break Google sign-in or token refresh
on iOS.
>
> **Overview**
> Adds persisted *seedless onboarding OAuth context* to Redux (new
`SET/CLEAR_SEEDLESS_ONBOARDING` actions + reducer state) and clears it
when restarting onboarding or deleting/resetting a wallet.
>
> Updates iOS Google OAuth to *switch between legacy iOS
redirect/clientId and web/universal-link credentials* via a new
`getIosGoogleConfig()` helper and legacy feature flag logic (with an iOS
< 17.4 safety fallback), while unifying Google web constants/redirect
naming.
>
> Ensures refresh-token requests on iOS Google reuse the original
`client_id` by reading the persisted onboarding clientId (fallbacking to
legacy `IosGID`), and updates OAuth authentication to pick iOS vs
Android auth-connection IDs based on device/clientId. Tests were
expanded/updated to cover these paths (including Google prompt
select-account and state reset).
>
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
24579e7. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->