Gem::ConfigFile#set_api_key

# File tmp/rubies/ruby-3.0.5/lib/rubygems/config_file.rb, line 317
def set_api_key(host, api_key)
  check_credentials_permissions

  config = load_file(credentials_path).merge(host => api_key)

  dirname = File.dirname credentials_path
  require 'fileutils'
  FileUtils.mkdir_p(dirname)

  Gem.load_yaml

  permissions = 0600 & (~File.umask)
  File.open(credentials_path, 'w', permissions) do |f|
    f.write config.to_yaml
  end

  load_api_keys # reload
end