[iOS] Add an explicit "Block connections without VPN" setting to VPN (VPN Kill Switch Toggle)

[soner-yuksel]

Resolves brave/brave-browser#38057

Design: https://www.figma.com/design/J4LKBMftiWhqromRWfUQLG/VPN-design?node-id=113-12449&t=PYj40XUIRVEX2lF6-0

Security Ticket: https://github.com/brave/reviews/issues/1689

This PR is adding the toggle for VPN kill switch which is an security feature designed to protect your digital data from accidental exposure.

The idea is when the VPN connection drops, the VPN kill switch will block your internet access until the connection to the VPN server is restored.

To build a VPN client that implements a packet-oriented, custom VPN protocol, a packet tunnel provider should be implemented.

To configure this an tunnel provider object should be created and this will manage the tunnel provider’s VPN configuration.

For IKEv2 this is NEVPNManager https://developer.apple.com/documentation/networkextension/nevpnmanager/
Usage in https://github.com/GuardianFirewall/GuardianConnect/blob/3c828f38094debd22d217ee61c0ecf05d76cd741/GuardianConnect/Classes/GRDVPNHelper.m#L728C2-L728C14

For WireGuard this is NETunnelProviderManager https://developer.apple.com/documentation/networkextension/netunnelprovidermanager
Usage in Guardian: https://github.com/GuardianFirewall/GuardianConnect/blob/3c828f38094debd22d217ee61c0ecf05d76cd741/GuardianConnect/Classes/GRDVPNHelper.m#L1001C72-L1001C95

And after that the protocol object needs to be created and set as protocol configuration for tunnel manager.

For WireGuard: NETunnelProviderProtocol https://developer.apple.com/documentation/networkextension/netunnelproviderprotocol
Usage in Guardian: https://github.com/GuardianFirewall/GuardianConnect/blob/3c828f38094debd22d217ee61c0ecf05d76cd741/GuardianConnect/Classes/GRDVPNHelper.m#L881C3-L881C27

And for IKEv2: NEVPNManager will assign the protocol configuration
Usage in Guardian:
https://github.com/GuardianFirewall/GuardianConnect/blob/3c828f38094debd22d217ee61c0ecf05d76cd741/GuardianConnect/Classes/GRDVPNHelper.m#L676

Finally to achieve the Kill Switch "Block connections without VPN" setting, the includeAllNetworks property should be set on protocol config.

NEVPNProtocol includeAllNetworks
https://developer.apple.com/documentation/networkextension/nevpnprotocol/3131931-includeallnetworks

The definition of includeAllNetworks is

If this property is true, the system routes network traffic through the tunnel except traffic for designated system services necessary for maintaining expected device functionality.

Guardian Side
IKEv2: https://github.com/GuardianFirewall/GuardianConnect/blob/3c828f38094debd22d217ee61c0ecf05d76cd741/GuardianConnect/Classes/GRDVPNHelper.m#L801
Wireguard: https://github.com/GuardianFirewall/GuardianConnect/blob/3c828f38094debd22d217ee61c0ecf05d76cd741/GuardianConnect/Classes/GRDVPNHelper.m#L1021

For Brave iOS implementation we can not just enable the includeAllNetworks and actually expect it will perform as requested.

After enabling key part is to establish a new connection entirely with this setting disabled or enabled.

Security Review: TBD

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Screenshots:

RPReplay_Final1720729393.MP4

Test Plan:

So the plans on QA side is to be related about being sure if the VPN can be switched on or off properly after enabling toggle

• Navigate Settings
• VPN Settings
• Enable and Disable Kill Switch
• Check VPN connection is established

[brave-builds]

A Storybook has been deployed to preview UI for the latest push