Two hop SSH with multiple user names

Question

I am trying to set up an ssh proxycommand, where the user name at the final host is different from the user name at the original host. I am logged in on firstHost as username and want to effectively run this command:

ssh middle ssh othername@target

I would like to be able to do this with

ssh target

This post suggests using a proxycommand that does an ssh to target to run nc on target. That makes the connection, but does not use the passwordless ssh that I set up. Is there a way to get this to work with passwordless ssh? (And is there a reason to use nc instead of making the proxy command ssh middle ssh othername@target?)

.ssh/config on firstHost looks like this:

Host middle
HostName middle.domain

Host target
User othername
Proxycommand ssh middle ssh [email protected] nc localhost 22

The output of ssh -vv target from firsthost is

debug2: ssh_connect: needpriv 0
debug1: Executing proxy command: exec ssh middle ssh [email protected] nc localhost 22
debug1: identity file /home/username/.ssh/identity type -1
debug2: key_type_from_name: unknown key type '-----BEGIN'
debug2: key_type_from_name: unknown key type '-----END'
debug1: identity file /home/username/.ssh/id_rsa type 1
debug1: identity file /home/username/.ssh/id_dsa type -1
debug1: loaded 3 keys
login banner from middle
login banner from target
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3
debug1: match: OpenSSH_4.3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_4.3
debug2: fd 5 setting O_NONBLOCK
debug2: fd 4 setting O_NONBLOCK
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: kex_parse_kexinit: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes256-ctr
debug2: kex_parse_kexinit: aes256-ctr
debug2: kex_parse_kexinit: hmac-sha1
debug2: kex_parse_kexinit: hmac-sha1
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: 
debug2: kex_parse_kexinit: first_kex_follows 0 
debug2: kex_parse_kexinit: reserved 0 
debug2: mac_init: found hmac-sha1
debug1: kex: server->client aes256-ctr hmac-sha1 none
debug2: mac_init: found hmac-sha1
debug1: kex: client->server aes256-ctr hmac-sha1 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<4096<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug2: dh_gen_key: priv key bits set: 275/512
debug2: bits set: 1987/4096
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host 'target' is known and matches the RSA host key.
debug1: Found key in /home/username/.ssh/known_hosts:16
debug2: bits set: 2053/4096
debug1: ssh_rsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug2: cipher_init: set keylen (16 -> 32)
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug2: cipher_init: set keylen (16 -> 32)
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /home/username/.ssh/identity ((nil))
debug2: key: /home/username/.ssh/id_rsa (0x2b9c1e95c4d0)
debug2: key: /home/username/.ssh/id_dsa ((nil))
login banner
debug1: Authentications that can continue: publickey,gssapi-with-mic,password
debug1: Next authentication method: gssapi-with-mic
debug1: An invalid name was supplied
Hostname cannot be canonicalized

debug1: An invalid name was supplied
Hostname cannot be canonicalized

debug1: An invalid name was supplied
Hostname cannot be canonicalized

debug2: we did not send a packet, disable method
debug1: Next authentication method: publickey
debug1: Trying private key: /home/username/.ssh/identity
debug1: Offering public key: /home/username/.ssh/id_rsa
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey,gssapi-with-mic,password
debug1: Trying private key: /home/username/.ssh/id_dsa
debug2: we did not send a packet, disable method
debug1: Next authentication method: password

Answer 1

alias sshTarget="ssh -tA middle ssh -l othername target"

Update

ssh -N -L 4441:othername:22 middle 
scp -P 4441 /documents/foo localhost:/backup/

Answer 2

In 2016, SSH added some shortcuts to make it dead simple. Instead of your ProxyCommand with netcat, just put ProxyJump middle in the Host block for "target." Each server can have its own user and almost any other parameter from ssh_config(5). You can chain hops together, too.

If you don't want to set up the config, you can do it all on the CLI with -J:

ssh -J me@middle othername@target

But you should set up the config. Then all you need to type is ssh target and everything works transparently.