Added ssh key import feature in "key import"

[adyxax]

What this PR does / why we need it:
This PR allows admins to import an existing ssh private key (typically needed when testing sshportal in an existing environment).

Special notes for your reviewer:
I don’t know if this feature is wanted, but we found it quite useful. I couldn't find a contributing guide, but I'm of course open to any code change that may be needed to properly integrate this code in the project.

[moul]

Nice, can you add a small usage example somewhere (readme, example dir or in this PR) ?

Thanks :)

[adyxax]

I am glad the feature is of interest to you.

I added a small change to the readme to document the "key import", here is an example run :

julien@andromeda:~/prog/go/src/github.com/moul/sshportal$ ssh -p2222 localhost -l julien


    __________ _____           __       __
   / __/ __/ // / _ \___  ____/ /____ _/ /
  _\ \_\ \/ _  / ___/ _ \/ __/ __/ _ '/ /
 /___/___/_//_/_/   \___/_/  \__/\_,_/_/


config> key import --name="test"
Paste your key and end with a blank line> -----BEGIN RSA PRIVATE KEY-----
Paste your key and end with a blank line> MIIEogIBAAKCAQEAv2yatLaFMtuBYZd3Cmnn9VcItANwT2AOxX18DNwX4evYtOEx
Paste your key and end with a blank line> jyEBkcBN+zAhbi6mClHUNfZSs+jQTIblpdzjDSxHHlRG3j/03U5Wa3fkXC4xKm1u
Paste your key and end with a blank line> eHSG+OC6QpoYtaEPyG9RZ11Zn/IWS6FPgmL8ysAjwzqU+CSO5qdM3nHXJI9w1U3C
Paste your key and end with a blank line> x8hQlNf1052oZihHe0CYx+5j+orUGA0+5qoiwgz9bIZKFTKSN22+oAaTIIw1nBFk
Paste your key and end with a blank line> CvxoauHopqIqvmhrRozGxVzNFhCJCxTaJaO3CV0sdSlFtYQjgSz3ZQEbIvg8+L9S
Paste your key and end with a blank line> 9TCNn8mgHaaEqQN6zVS2eDBm6cnIqtkcozpA5wIDAQABAoIBADW+aDEUjZEZz9l2
Paste your key and end with a blank line> jRV/ZoCbTvY7gOzIK12HPazenlXvwYgHMcLdoXMqarp7aOdmcXe0QcBkyBN66gCS
Paste your key and end with a blank line> XyeSPK0WIWGCh+MeUcFQnTLPFm5LCcK/tqRbEwoNDj5kxUs5TRUZK+G5c9BUR640
Paste your key and end with a blank line> O/5/jDngeCn36JtCqFxZ3FsX2y+IGeAHOLrMsfop4N1lIGDC8QsRazGVK6Z/bkUX
Paste your key and end with a blank line> Bn/QnPOIUBGjYNn490mNZLFrZ29XPXtvEA5vkiAsKCpQeMqT/AO/zL+mVdWJ4k7o
Paste your key and end with a blank line> ckXE2gysJTqtFnTBv9CT2BiWhXr2D0qXiGgu4H6xYUbLUVLMVINpyBytb7NDL983
Paste your key and end with a blank line> bxkbrgECgYEA5hthgOYGA16uVzhLpq8tdKI0wAoKQgMYlocfhCL1qRL62PPeUOdv
Paste your key and end with a blank line> GdfO5ohdF86SHhp/uAHa6VioKc1JWP4om4FhDn8ZnxrBaDqxsPP0YyshRSe8Ge4I
Paste your key and end with a blank line> m7Om1FFckUMbF6cz1+fjfU5y5hut+k/pbNE9eih1iIM4OfnXTcoRZh8CgYEA1Pbn
Paste your key and end with a blank line> A/fxwxlH9qiX79L7d2IjlCLzTv5qYgLUotmk8A3UNQdM5EpX7sQsq5ZTNX6EYEMQ
Paste your key and end with a blank line> Zivc7NIjXl6Rw5Koyorn0TbcCRYGq9J2u+sEz9cGOnaTqqP5PaRKW3JFSfcTw86O
Paste your key and end with a blank line> VTZh3kO7ypbxhtAB6UIDfFU3zXkBQ2qPohis/DkCgYANGnoO8QpensGmzdnhABDC
Paste your key and end with a blank line> l4oRdYDoCW0ZBVDSIXuDyUTnnduHF+bHvfZWQmWquWSwuimTvOdOanIJD1uh6bc+
Paste your key and end with a blank line> Q7vXK322BbwFx3He9cVw8D/QxFZ904RB+ZUCei+fRgcA7dCR9u6JcDIy0Fiz7GEK
Paste your key and end with a blank line> hU/O6QboYzCMfKG6GEutWQKBgCzzZHWQ+yWsC2WD1nYXeV6Mh2f4LJUK3FeNs2Yg
Paste your key and end with a blank line> PFEzCgybWt6A1qieHbOmCjArYTOUVDzMm1gdTrvXiDrYlOoTgbTGOJFuZcAUr10g
Paste your key and end with a blank line> 0SYxg64JY0fMTop1SACfUQK4tSJKUf6oeOXaNCQh0h8bfpvGhEfVEO880EhzkJet
Paste your key and end with a blank line> T635AoGAR1T58battIKUn0PO0afvU1zgE/mFNYn2PFuBTHdDJxrBOp64lV76s8x5
Paste your key and end with a blank line> jiYPjSOIQ0JGzUkDhvwIIZg0pu7FevLlBbK6AiufU59wT2dsCMgg46VafpPpn9VB
Paste your key and end with a blank line> hsVwCYFurjhPeVNNWzsK39KW8g0AC4MIOTvm607Pv1g6PxP2v8E=
Paste your key and end with a blank line> -----END RSA PRIVATE KEY-----
Paste your key and end with a blank line>
11
config> key ls
  ID |  NAME   | TYPE | LENGTH | HOSTS |    UPDATED     |    CREATED     |       COMMENT
+----+---------+------+--------+-------+----------------+----------------+----------------------
  11 | test    | rsa  |   2048 |     0 | 10 seconds ago | 10 seconds ago |
   7 | adyxax  | rsa  |   4096 |     1 | 20 hours ago   | 20 hours ago   |
   2 | host    | rsa  |   2048 |     0 | 1 day ago      | 1 day ago      | created by sshportal
   1 | default | rsa  |   2048 |     0 | 1 day ago      | 1 day ago      | created by sshportal
Total: 4 keys.
config>

I wanted to add this run to the integration tests but couldn't figure out how to properly run thos tests : the testserver keeps crashing shortly after the docker-compose up on my setup with the following error :

julien@XXX:~/prog/go/src/github.com/moul/sshportal/examples/integration$ docker-compose up testserver
Recreating integration_testserver_1 ...
Recreating integration_testserver_1 ... done
Attaching to integration_testserver_1
testserver_1  | 2018/03/12 13:19:31 starting ssh server on port 2222...
testserver_1  | panic: runtime error: slice bounds out of range
testserver_1  |
testserver_1  | goroutine 37 [running]:
testserver_1  | main.testServer.func1(0x9f8aa0, 0xc4202be840)
testserver_1  |         /go/src/github.com/moul/sshportal/hidden.go:34 +0x9a4
testserver_1  | github.com/moul/sshportal/vendor/github.com/gliderlabs/ssh.(*session).handleRequests.func1(0xc4202be840)
testserver_1  |         /go/src/github.com/moul/sshportal/vendor/github.com/gliderlabs/ssh/session.go:219 +0x3b
testserver_1  | created by github.com/moul/sshportal/vendor/github.com/gliderlabs/ssh.(*session).handleRequests
testserver_1  |         /go/src/github.com/moul/sshportal/vendor/github.com/gliderlabs/ssh/session.go:218 +0x1ff
integration_testserver_1 exited with code 2

With some debugging I managed to isolate the fact that the healthcheck call from docker is the cause of the problem, the testserver sees it without arguments and the s.Command()[1:] on hidden.go:33 fails.

[ivomarino]

useful feature, thanks, when will this be merged? thanks

[adyxax]

I updated my pull request by rebasing on top of the last commits.