lfshttp: pass stdin to ssh

Some people have SSH prompt them for their passphrase when a key is
used. In such a situation, the user needs to be able to enter a password
on standard input so that they can use their key. When invoking ssh,
pass our standard input through to the ssh process so that it can prompt
the user if needed.

lfshttp/ssh.go

@@ -4,6 +4,7 @@ import (
	"bytes"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
@@ -87,6 +88,7 @@ func (c *sshAuthClient) Resolve(e Endpoint, method string) (sshAuthResponse, err

	// Save stdout and stderr in separate buffers
	var outbuf, errbuf bytes.Buffer
	cmd.Stdin = os.Stdin
	cmd.Stdout = &outbuf
	cmd.Stderr = &errbuf