feat(mobile): add server cert field, similar to client cert

[crisoagf]

Initial code for server certificate field.

[zackpollard]

Hey, could you please provide more information on what this is supposed to achieve?

[crisoagf]

Hey, could you please provide more information on what this is supposed to achieve?

Sure thing!

This is an attempt to implement certificate selection for self-signed/enterprise-signed servers without simply disabling SSL certificate checking. It creates another settings field, similar to the client certificate selection, to import a root or self-signed certificate and use that for connection validation. AFAICT, this is only needed for Android, for iPhones already respect user imported certificates.

Currently, the only option for custom root certs or self-signed certs in Android is "Allow self-signed SSL certificates" that accepts any certificate that matches the hostname, which is at least a bit scary from an MITM attack perspective.

Context is #13555 .

[alextran1502]

Hello, can you add some information on how this PR has been tested?

[crisoagf]

So far I tested with local build + flutter run. Try to use without given code doesn't work, with given code works.

I'll try to add some info in some file in the repo and I'd really like to write a couple of tests. I may take a while (haven't been having a lot of free time lately), but I'll do it.