Gem::ConfigFile#set_api_key

# File tmp/rubies/ruby-4.0.0/lib/rubygems/config_file.rb, line 339
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)

  permissions = 0o600 & ~File.umask
  File.open(credentials_path, "w", permissions) do |f|
    f.write self.class.dump_with_rubygems_yaml(config)
  end

  load_api_keys # reload
end