Every time I go to add a mirror, I got to Diffusion first, click Add Mirror and then remember that this dialog doesn't let me create a new credential. So then I have to navigate back to applications, to Passphrase, create the new credential, save it, copy the public key to GitHub (I have to do this regardless, but there's a lot more steps before and after this), save the credential, find the repository in Diffusion again and then go back to the Add Mirror workflow so it appears in the drop-down.

Often when I'm setting up a mirror I don't want to use an existing key (in fact, I don't think I've *ever* used an existing key). I always just want to make a new key and copy the public key to GitHub.