Estou usando o Paramiko para executar scripts bash em um servidor remoto. Em alguns desses scripts, há conexões ssh com outros servidores. Se eu usar apenas bash, sem Python, minha chave DSA será encaminhada e usada pelo script bash no primeiro servidor remoto para conectar-se ao segundo servidor remoto. Quando uso Paramiko, não é o caso.

Exemplo de festança:

Jean@mydesktop:~ & ssh root@firstserver
root@firstserver:~ # ssh root@secondserver hostname
secondserver.mydomain.org

Usando Paramiko:

#!/usr/bin/python3
# -*- coding: utf-8 -*-

import paramiko

class SSHSession:


    def __init__(self, server_address, user='root', port=22):
        self.connected = False
        self.server_address = server_address
        self.user           = user
        self.port           = port


    def connect(self, clear_channel=True):
        try:
            if self.server_address == None:
                raise ValueError('No hostname')
        except:
            raise ValueError('No hostname')
        else:
            try:
                self.ssh_client = paramiko.SSHClient()
                self.ssh_client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
                self.ssh_client.connect(self.server_address, username=self.user)
                #self.transport = self.ssh_client.get_transport()
                #self.channel   = self.transport.open_forward_agent_channel()
                self.channel   = self.ssh_client.invoke_shell()
            except:
                self.connected = False
                return False
            else:
                self.connected = True
                return True

    def exec_command(self, command, newline='\r'):
        if not self.connected:
            raise Exception('Not connected')
        else:
            timeout = 31536000 # 365 days in seconds
            self.channel.settimeout(timeout)
            line_buffer    = ''
            channel_buffer = ''
            end_string     = 'CLIENT_EXPECT_CMD_OK'
            print('[SEND   ] >>', command)
            self.channel.send(command + ' ; echo ' + end_string + newline)
            while True:
                channel_buffer = self.channel.recv(1).decode('UTF-8')
                if len(channel_buffer) == 0:
                    raise Exception('connection lost with server: ' + self.server_address)
                    break 
                channel_buffer  = channel_buffer.replace('\r', '')
                if channel_buffer != '\n':
                    line_buffer += channel_buffer
                else:
                    if line_buffer == end_string:
                        break
                    print('[RECEIVE] <<', line_buffer)
                    line_buffer   = ''


    def disconnect(self):
        self.ssh_client.close()


    def __enter__(self):
        self.connect()
        return self


    def __exit__(self, _type, value, traceback):
        self.disconnect()


if __name__ == "__main__":
    server_address = 'firstserver'
    ssh_user       = 'root'
    with SSHSession(server_address) as ssh_session:
        ssh_session.exec_command('hostname')
        ssh_session.exec_command('ssh root@secondserver hostname')

A saída é:

[SEND   ] >> hostname
[RECEIVE] << [root@firstserver ~]# hostname ; echo CLIENT_EXPECT_CMD_OK
[RECEIVE] << firstserver.mydomain.fr
[SEND   ] >> ssh root@secondserver hostname
[RECEIVE] << [root@firstserver ~]# ssh root@secondserver hostname ; echo CLIENT_EXPECT_CMD_OK
[RECEIVE] << Permission denied (publickey,gssapi-keyex,gssapi-with-mic).

Eu tentei:

self.transport = self.ssh_client.get_transport()
self.channel   = self.transport.open_forward_agent_channel()

ao invés de :

self.channel   = self.ssh_client.invoke_shell()

mas então eu recebo um erro:

paramiko.ssh_exception.ChannelException: Administratively prohibited

Alguém sabe se isso é possível? Encontrei discussões sugerindo que é isso, mas ainda não sei como fazer isso.