HowTo: Set contextual git identities

This post is a follow-up to the HowTo: Set contextual git configurations one. And it won’t be a surprise, but I chose to share it primarily for my future self since the topic is pretty easy to find using a search engine, but everybody calls it differently.

The problem

If you didn’t know, services like GitHub and GitLab associate the private encryption key you provided to them in a 1-to-1 relationship with your account. In other words, if you have multiple accounts on said platform and your preferred git transport is SSH, you must create and upload a key pair for each account.

Honestly, creating and uploading key pairs is a trivial process. However, from time to time, you could forget to set the correct identity on your ssh-agent before doing a git push, and then you have the unsettling situation where your PR looks like someone else tried to hijack your work.

The good thing is that we have ways to work around this.

Solution 1 - Override the ssh-agent configurations

Let’s say you have two GitHub (or GitLab) accounts iDev and iCorpDev respectively, from which you want to use the latter as the default one.

Create the ssh key pair for each account. (ie: id_rsa_me and id_rsa_corp)
Upload the respective private key to each of the GitHub accounts
Create an ssh configuration file (~/.ssh/config) if there isn’t one already
Add ssh configuration entries for each of those GitHub accounts (see the code snippet below) a. Make sure each uses a different Host identifier, which must be an FQDN b. Make sure both have github.com as its Hostname
You are set! But remember to use the correct URLs when cloning a. The URI [email protected]:an-owner/a-repository.git will make the ssh-agent to use id_rsa_corp b. The URI [email protected]:an-owner/a-repository.git will make the ssh-agent to use id_rsa_me

# Identify as iCorpDev
Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_corp

# Identify as iDev
Host me.github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_me

If you haven’t spotted the trick yet, it is on the domain your git remote is using when cloning personal projects, which for the example above, will be me.github.com. Worth noting that the domain you’ll use does not even have to exist as long we have the correct one in the Hostname field, and its only purpose is to let the ssh-agent know the configuration we are requesting it to use.

Solution 2 - Use HTTPS and GitHub Personal Access Tokens

First, this only works for GitHub, and for this scenario, let’s say you have two accounts iDev and iCorpDev respectively, from which you want to use the latter as the default one.

On GitHub, create a personal access token only for your personal account. (reference)
On your terminal, configure git to use the iDev user and the Access Token as its password (see the code snippet below) every time you interact with a repository with a remote prefixed with https://github.com/iDev.
Try it out! Once you clone over HTTPS transport, git will automatically know which credentials to use.

# For this example the user will be "iDev" and the token "a-fake-token".
# Please update them accordingly
$ GH_USER='iDev'
$ GH_TOKEN='a-fake-token'
$ git config --global --add url."https://${GH_USER}:${GH_TOKEN}@github.com/${GH_USER}".insteadOf "https://github.com/${GH_USER}"

For anything else that is not your iDev account, git will ask you for credentials. Still, for that matter, you could either configure the other account credentials globally or use the SSH key as usual.

Conclusion

I don’t think either solution is a clear-cut one, so it is up to you to pick the one that fits better with you. Before I forget, let me share the credit with the following posts that allowed me to learn about these approaches:

Last modified on 2022-02-06