* Allow vault ssh to accept ssh commands in any ssh compatible format
Previously vault ssh required ssh commands to be in the format
`username@hostname <flags> command`. While this works just fine for human
users this breaks a lot of automation workflows and is not compatible
with the options that the ssh client supports.
Motivation
We currently run ansible which uses vault ssh to connect to hosts.
Ansible generates ssh commands with the format `ssh <flags> -o User=username hostname
command`. While this is a valid ssh command it currently breaks with
vault because vault expects the format to be `username@hostname`. To work
around this we currently use a wrapper script to parse the correct username being set
by ansible and translate this into a vault ssh compatible `username@hostname` format
Changes
* You can now specify arguments in any order that ssh client allows. All
arguments are passed directly to the ssh command and the format isn't
modified in any way.
* The username and port are parsed from the specified ssh command. It
will accept all of the options supported by the ssh command and also
will properly prefer `-p` and `user@` if both options are specified.
* The ssh port is only added from the vault credentials if it hasn't
been specified on the command line
