Manage Multiple SSH Keys With Different Hosts

Private and corporate github accounts and repositories may be set up with different SSH keys. This post outlines briefly how I configure SSH to make the switching transparent.

Multiple different SSH key pairs may have been imported or created with

ssh-keygen -t rsa -C "email@example.org"

Create a local SSH config

touch ~/.ssh/config

Assuming we have two github accounts, a private one and a corporate one, I'd set the default to the keypair `id_rsa` here for the default `github.com` host.

Corporate repositories will use the `github.com-corpo` repository url.

Host github.com
        HostName github.com
        IdentityFile ~/.ssh/id_rsa
Host github.com-corpo
        HostName github.com
        IdentityFile ~/.ssh/id_ed25519

We'd then clone repositories using the identifier host:

git clone git@github.com-corpo:some-corporation/some-repo.git

Or update the repository config under `.git/config` then gets the remote url set as follows:

[remote "origin"]
        url = git@github.com-corpo:some-corporation/some-repo.git
        fetch = +refs/heads/*:refs/remotes/origin/*

Go Private Dependencies

With the above setup Go private dependencies may fail on `go mod tidy` with:

go: finding module for package github.com/corpo/repository/api
go: downloading github.com/corpo/repository v0.0.0-20220309104613-82b02c89f961
github.com/corpo/my-other-repository/package imports
        github.com/corpo/repository/api: github.com/corpo/repository@v0.0.0-20220309104613-82b02c89f961: verifying module: github.com/corpo/repository@v0.0.0-20220309104613-82b02c89f961: reading https://sum.golang.org/lookup/github.com/corpo/repository@v0.0.0-20220309104613-82b02c89f961: 410 Gone
        server response:
        not found: github.com/corpo/repository@v0.0.0-20220309104613-82b02c89f961: invalid version: git fetch -f origin refs/heads/*:refs/heads/* refs/tags/*:refs/tags/* in /tmp/gopath/pkg/mod/cache/vcs/f7223b0c74f927514a7dcf6437bf4284cb35c4f028686b6b2cd906e7379439d9: exit status 128:
                fatal: could not read Username for 'https://github.com': terminal prompts disabled

Ensure your `~/.gitconfig` has the overrides in the order of matching from more details to less, e.g.:

[url "git@github.com-corpo:corpo"]
	insteadOf = https://github.com/corpo
[url "git@github.com:corpo"]
	insteadOf = https://github.com/corpo
[url "git@github.com:"]
	insteadOf = https://github.com/

Then mark the repository path as private, here on the entire corporation:

export GOPROXY=direct
export GOPRIVATE=github.com/corpo

Now `go mod tidy` should succeed.

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