Add support for Git Credential Manager Core as a credential helper option

[mjcheetham]

Add Git Credential Manager (GCM) Core to the Git for Windows installer.
GCM Core is the cross-platform credential helper that will eventually
replace the exiting GCM for Windows (and GCM for Mac/Linux) helpers.

Move the "Enable Git Credential Manager" option to its own, new page
where you can select between the three options: none, GCM, or GCM Core.

Reusing the same "Use Credential Manager" replay choice key, we can
ensure that existing choices for GCM for Windows are carried forwards to
the new three-option choice. Enabled = GCM for Windows, Disabled = None,
and a new option Core = GCM Core.

Because GCM Core is still in beta we do not make it the default yet; GCM
for Windows is the default.

Signed-off-by: Matthew John Cheetham mjcheetham@outlook.com

[PhilipOakley]

Is there a wider justification to be added to the commit - it's worth starting the commit explanation even if it's still wip.

Don't assume everyone is familiar with the abbreviations, or the potential benefits, and don't forget to include any documentation improvement that will guide the users to use the benefits...

[dscho]

I agree that there could be a justification (it's easy to see: Git Credential Manager for Windows is limited to Windows, whereas the Core version can replace that totally stale Java version of the Git Credential Manager).

Also, could you make this a radio button choice between GCM Windows, GCM Core and "leave unconfigured", moving it to a new page?

[mjcheetham]

Hi @PhilipOakley, sorry for not being more descriptive with this change. It is indeed a work-in-progress, and was directed at @dscho for some initial comments which we also had offline - I realise this lack of context for others on GitHub is not a good thing. I hoped creating the PR as draft would also help indicate as such.

The benefits are that we plan to deprecate the existing Git Credential Manager for Windows and replace it with Git Credential Manager Core, the cross-platform replacement which will receive more support, fixes and features in the future.

I wanted to get Git Credential Manager Core into the Git for Windows installer as an experimental option at first to help provide a limited rollout of the component that is yet to see wide-spread testing.

@dscho I agree that a separate page for selecting a credential helper ("None/unset", "GCM for Windows", or "GCM Core [experimental]") would probably be better. We should also be able to reuse the existing stored preference for "Use Credential Manager" and extend it to include a "core" value.

[dscho]

Just a couple minor suggestions. Please let me know if you agree.

[dscho]

Awesome job, @mjcheetham!

[yyjdelete]

@mjcheetham @dscho
Question: Seems the option is not shown when Only show new options is enabled in new released git-for-windows 2.28.0-x64?

[rimrul]

Yes. That's due to the way Only show new options works. It doesn't realise there's a new answer for the credential manager. It only realises that we previously asked you about the credential manager.

[nkjackzhang]

When i use git help credential-manager-core, i get error like Can't find file C:/Program Files/Git/mingw64/share/doc/git-doc/git-credential-manager-core.html, is it missing?

[rimrul]

I don't think such a help file exists.