feat: Add username-router plugin for SSHPiper to route connections based on username (#599)

* feat: Add username-router plugin for SSHPiper to route connections based on username

* feat: Add username-router plugin to GoReleaser configuration

plugin/username-router/README.md

@@ -0,0 +1,11 @@
+# username-router plugin for sshpiper
+
+Supports routing based on username. This plugin allows you to route connections to different targets based on the username provided during the SSH connection.
+The username format is `target+username`, where `target` is the target host and `username` is the username to use for that target.
+`target` can be an IP address or a hostname, and it can also include a port number in the format `target:port`.
+
+## Usage
+
+```
+sshpiperd username-router
+```

plugin/username-router/main.go

@@ -0,0 +1,59 @@
+//go:build full || e2e
+
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/tg123/sshpiper/libplugin"
+	"github.com/urfave/cli/v2"
+)
+
+func parseTargetUser(raw string) (target string, username string, err error) {
+	// Expect format: [target:port]+user
+	parts := strings.SplitN(raw, "+", 2)
+	if len(parts) != 2 {
+		err = fmt.Errorf("invalid format (expected target:port+user)")
+		return
+	}
+
+	target = parts[0]
+	username = parts[1]
+	return
+}
+
+func main() {
+
+	libplugin.CreateAndRunPluginTemplate(&libplugin.PluginTemplate{
+		Name:  "username-router",
+		Usage: "routing based on target inside username, format: 'target:port+realuser@sshpiper-host'",
+		CreateConfig: func(c *cli.Context) (*libplugin.SshPiperPluginConfig, error) {
+
+			return &libplugin.SshPiperPluginConfig{
+				PasswordCallback: func(conn libplugin.ConnMetadata, password []byte) (*libplugin.Upstream, error) {
+
+					address, user, err := parseTargetUser(conn.User())
+					if err != nil {
+						return nil, fmt.Errorf("invalid username format %q: %w", conn.User(), err)
+					}
+
+					host, port, err := libplugin.SplitHostPortForSSH(address)
+					if err != nil {
+						return nil, fmt.Errorf("invalid target address %q: %w", address, err)
+					}
+
+					log.Info("routing to address ", address, " with user ", user)
+					return &libplugin.Upstream{
+						UserName:      user,
+						Host:          host,
+						Port:          int32(port),
+						IgnoreHostKey: true,
+						Auth:          libplugin.CreatePasswordAuth(password),
+					}, nil
+				},
+			}, nil
+		},
+	})
+}