ssh: Implement authentication for new ssh server

internal/dis/component/ssh/ssh.go

@@ -0,0 +1,104 @@
+package ssh
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"io"
+
+	"github.com/FAU-CDI/wisski-distillery/internal/dis/component"
+	"github.com/FAU-CDI/wisski-distillery/internal/dis/component/instances"
+	"github.com/FAU-CDI/wisski-distillery/pkg/sshx"
+	"github.com/gliderlabs/ssh"
+	"github.com/tkw1536/goprogram/stream"
+	"github.com/tkw1536/proxyssh/feature"
+)
+
+type SSH struct {
+	component.Base
+	Instances *instances.Instances
+}
+
+const (
+	etx rune = 3
+	eot rune = 4
+)
+
+const welcomeMessage = `Welcome to the WissKI SSH Server.
+You've successfully authenticated, but we don't provide shell access to the main server.
+You may use this connection as part of a proxy jump to connect to your server.
+For example: 
+
+ssh -J %s:2222 www-data@%s
+
+Press CTRL-C to close this connection.
+`
+
+// Server returns an ssh server that implements the main ssh server
+func (s *SSH) Server(context context.Context, ios stream.IOStream) (*ssh.Server, error) {
+	var server ssh.Server
+
+	banner := fmt.Sprintf(welcomeMessage, s.Config.DefaultDomain, "example."+s.Config.DefaultDomain)
+
+	server.Handle(func(session ssh.Session) {
+		io.WriteString(session, banner)
+
+		buffer := bufio.NewReader(session)
+		for {
+			res, _, err := buffer.ReadRune()
+			if err != nil {
+				return
+			}
+			if res == etx || res == eot {
+				return
+			}
+		}
+
+	})
+	server.PublicKeyHandler = feature.AuthorizeKeys(
+		slogger{IOStream: ios},
+		func(ctx ssh.Context) (keys []ssh.PublicKey, err error) {
+			keys, err = s.GlobalKeys()
+			if err != nil {
+				return nil, err
+			}
+
+			instances, err := s.Instances.All()
+			if err != nil {
+				return nil, err
+			}
+
+			for _, instance := range instances {
+				ikeys, err := instance.SSH().Keys()
+				if err != nil {
+					continue
+				}
+				keys = append(keys, ikeys...)
+			}
+			return keys, nil
+		})
+	return &server, nil
+}
+
+func (s *SSH) GlobalKeys() ([]ssh.PublicKey, error) {
+	file, err := s.Environment.Open(s.Config.GlobalAuthorizedKeysFile)
+	if err != nil {
+		return nil, err
+	}
+	bytes, err := io.ReadAll(file)
+	if err != nil {
+		return nil, err
+	}
+	return sshx.ParseAllKeys(bytes), nil
+}
+
+type slogger struct {
+	stream.IOStream
+}
+
+func (s slogger) Print(v ...any) {
+	fmt.Fprint(s.Stderr, v...)
+}
+func (s slogger) Printf(format string, v ...any) {
+	fmt.Fprintf(s.Stderr, format, v...)
+}