I maintain and work on a number of repositories on BitBucket for both work and in my own time and use a separate account for each. SSH is used to talk with the remotes and I use my Multi SSH Key Manager to manage the keys.

The problem with this is that the remotes for all BitBucket repos have the same username and server git@bitbucket.org and as soon as I associate a key for git@bitbucket.org with my work account, I can't associate it with my personal account.

I could link the accounts together and then they could both use the same key but I want to keep them separate, so I needed to find a way of telling Git to use a certain key with a certain remote.

Here's how I did it...

How It Works

It was possible to solve this problem only because Git looks at the value of an environment variable called GIT_SSH_COMMAND when it calls SSH (see Requirements below). The way it works is that all calls to Git are intercepted with an alias, this alias then looks for the config variable SSH.keypath by calling git config -l and if the config variable has been defined we prefix the git command with the GIT_SSH_COMMAND set to ssh -i <SSH.keypath value>.

Why Can't You Just Add Another Key To Your .ssh Directory?

Good question. I could just generate a new key and stick it along side my default key but I am using my Multi SSH Key Manager that I wrote a little while back to help keep keys all separated and all the keys generated are in a subdirectory and SSH won't look recursively when trying to find keys to use.

Requirements

The GIT_SSH_COMMAND environment variable was only added in Git v2.3 so can only be used in v2.3 and above.

Cascading Config

I used git config -l to check for the existence of the config variable and the nice thing about this is that git config checks not only the config of the current repo but also the global Git config to, so you could for example define a default key in your global Git config (in ~/.gitconfig) and then override it where you need to

Limitations

Currently you can only define one key per repository and that one will be used when communicating with all the remotes, i'd like to have more granular control so I can give a list of remotes or remote names and specify a key for each and a default to fall back on.