git: login with deploy key

Generate a new ssh key:

ssh-keygen -t ed25519 -C "git@simpel.cc"

Name it like "id_github_server".

Adding your ssh key to the ssh-agent:

eval "$(ssh-agent -s)"

ssh-add ~/.ssh/id_github_server

Prepare ssh config:

vim ~/.ssh/config

Host github.com
  Hostname github.com
  User git
  AddKeysToAgent yes
  IgnoreUnknown UseKeychain
  UseKeychain yes
  IdentityFile ~/.ssh/id_github_server

Copy the ssh public key to your clipboard:

pbcopy < ~/.ssh/id_github_server.pub

Go to GitHub > Setting > Deploy keys and create e.g. "simpel.cc" and paste public key.

Make local repo ready for key use.

vim .git/config

Add to [core]:

sshCommand = "ssh -i ~/.ssh/id_github_server"

git config core.sshCommand "ssh -i ~/.ssh/id_github_mbax"

If [remote "origin]" is called by https change to ssh:

url = git@github.com:SimpelMe/REPO.git

You get this git-url with help of Code-(Clone)-Button > SSH on github.