net/ssh login with public key string

net-ssh-key.rb

host = 'host'
user = 'user'
options = {
  keys_only: true,
  keys: [],
  key_data: [ server_ssh_private_key ],
  user_known_hosts_file: [],
  known_hosts: Class.new do
    def self.search_for(host, options={})
      fingerprint = server_ssh_fingerprint.split(/\s+/).last
      key = Net::SSH::Buffer.new(fingerprint.unpack('m*').first).read_key
      Net::SSH::HostKeys.new([ key ], host, nil, options)
    end
  end,
  verify_host_key: :always,
}

Net::SSH.start(host, user, options) do |ssh|
end

Net::SFTP.start(host, user, options) do |sftp|
end