Problem

Git applies settings from your ~/.gitconfig to every repository. This is useful for defaults but becomes a problem when repositories or remotes need different identities or settings, for example:

1. Different user identities or signing keys for different remotes (github, gitlab, bitbucket).
2. Frequently switching between private and public remotes, which forces manual overrides.
3. Managing multiple SSH keys and per-host commit signing.

These situations often require editing or overriding your global config.

Using includeIf Conditional Configuration

Git's includeIf directive allows you to conditionally include configuration files based on certain criteria, such as the presence of a specific remote URL.

hasconfig:remote.*.url checks if any remote URL matches the specified pattern. This enables you to load different configuration files based on the remote repository's host.

How it works

• Use ~/.ssh/config to select the right SSH key per host.
• Use Git's includeIf to load host-specific .gitconfig only when a repository uses that remote.
• Configure commit signing per host and register allowed signers on the server.

This is for Windows, but the same principles apply to Linux and macOS. Just adjust file paths accordingly.

I am using different SSH keys for authentication and signing commits for GitHub and GitLab. You can use the same key for both, but I prefer separate keys.

Step-by-step setup

1. Create a SSH config file at ~/.ssh/config

# github
Host github.com
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_ed25519_github_auth
    IdentitiesOnly yes
 
# gitlab
Host gitlab.com
    HostName gitlab.com
    User git
    IdentityFile ~/.ssh/id_ed25519_gitlab_auth
    IdentitiesOnly yes

~/.ssh/config is optional but useful if you use different SSH keys for different hosts. It ensures the correct key is used for authentication.

2. Create a Git configuration file for GitLab at ~/.gitconfig-gitlab

[user]
	signingkey = C:\\Users\\username\\.ssh\\id_ed25519_gitlab_sign.pub

3. Update your global Git configuration at ~/.gitconfig to include the GitLab config when a repository uses a GitLab remote.

[user]
	name = thisisrick25
	email = swapnaneel06@gmail.com
	signingkey = C:\\Users\\username\\.ssh\\id_ed25519_github_sign.pub
[filter "lfs"]
	clean = git-lfs clean -- %f
	smudge = git-lfs smudge -- %f
	process = git-lfs filter-process
	required = true
[gpg]
	format = ssh
[commit]
	gpgsign = true
[includeIf "hasconfig:remote.*.url:*gitlab.com*/**"]
    path = ~/.gitconfig-gitlab
[includeIf "hasconfig:remote.*.url:https://gitlab.com/**"]
    path = ~/.gitconfig-gitlab

gitlab.com*/** is used for SSH remotes for GitLab. https://gitlab.com/** is used for HTTPS remotes for GitLab.