Likbez: ssh-agent x-session manager - why is it needed?

Question

SSH

Good night habrazhiteli!

Given
Clean Ubuntu 12.04
Installed xorg and lxde-core.
Ran startx
htop until heap showed another new process

/usr/bin/ssh-agent x-session-manager

How can this be used in practice? Why is it needed at all?

Please help in eliminating illiteracy

UPD
Practical application here

Answer 1

Not very clear in my previous post. The ability to run applications on a remote machine is a property of the X System architecture. SSH is only needed for authentication and data encryption. Telnet can be used as a session protocol instead of ssh.

Answer 2

So that X client applications running on a remote machine can connect to your X Server. The default authentication is SSH. ssh-agent is a key management utility.
For example, you have a system administration program running on a remote server. This program connects to the X Server on your local machine and allows you to configure the remote machine in graphical mode.

Answer 3

Actually ssh-agent is an analogue of Pageant from the PuTTY kit. Usage: we generate a private-public key pair on our machine, we protect the private key with a password during creation. We add the public key to .ssh/authorized_keys on remote machines.
We try to log in to remote machines and observe that if earlier it was necessary to enter a password from a remote user, now we need to enter a passphrase from a local private key. When you get tired of it, you can use Pageant or ssh-agent: run it, ask you to decrypt the private key into memory, enter passphrase, and since then, when accessing remote machines, passphrase is no longer required. ssh-agent keeps the decrypted private key in memory and allows third party processes to use it, but does not allow the key itself to be read.
If ssh-agent has a command (x-session-manager in our case), that command is run by a sub-process of ssh-agent, and ssh-agent will exit with that child process. It seems that ssh-agent is hung on X sessions in this way.
PS X11 Forwarding is another ssh feature. X11 clients authenticate with a magic cookie (.Xauthority), which usually only local processes started by the same user have access to. To prevent cookies from leaking to the left, as a security measure, ssh on the remote machine uses another cookie and, after checking, replaces it in the protocol with a local cookie.