Check and update Agent's Management URL if is legacy (#406)

All the existing agents by default connect to port 33073 of the
Management service. This value is also stored in the local config.
All the agents won't switch to the new port 443
unless explicitly specified in the config.
We want the transition to be smooth for our users, therefore
this PR adds logic to check whether the old port 33073 can be
changed to 443 and updates the config automatically.

client/internal/connect.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"github.com/netbirdio/netbird/client/ssh"
 	nbStatus "github.com/netbirdio/netbird/client/status"
+	mgmtcmd "github.com/netbirdio/netbird/management/cmd"
 	"strings"
 	"time"
 
@@ -239,3 +240,67 @@ func connectToManagement(ctx context.Context, managementAddr string, ourPrivateK
 
 	return client, loginResp, nil
 }
+
+// UpdateOldManagementPort checks whether client can switch to the new Management port 443.
+// If it can switch, then it updates the config and returns a new one. Otherwise, it returns the provided config.
+// The check is performed only for the NetBird's managed version.
+func UpdateOldManagementPort(ctx context.Context, config *Config, configPath string) (*Config, error) {
+
+	if config.ManagementURL.Hostname() != ManagementURLDefault().Hostname() {
+		// only do the check for the NetBird's managed version
+		return config, nil
+	}
+
+	var mgmTlsEnabled bool
+	if config.ManagementURL.Scheme == "https" {
+		mgmTlsEnabled = true
+	}
+
+	if !mgmTlsEnabled {
+		// only do the check for HTTPs scheme (the hosted version of the Management service is always HTTPs)
+		return config, nil
+	}
+
+	if mgmTlsEnabled && config.ManagementURL.Port() == fmt.Sprintf("%d", mgmtcmd.ManagementLegacyPort) {
+
+		newURL, err := ParseURL("Management URL", fmt.Sprintf("%s://%s:%d",
+			config.ManagementURL.Scheme, config.ManagementURL.Hostname(), 443))
+		if err != nil {
+			return nil, err
+		}
+		// here we check whether we could switch from the legacy 33073 port to the new 443
+		log.Infof("attempting to switch from the legacy Management URL %s to the new one %s",
+			config.ManagementURL.String(), newURL.String())
+		key, err := wgtypes.ParseKey(config.PrivateKey)
+		if err != nil {
+			log.Infof("couldn't switch to the new Management %s", newURL.String())
+			return config, err
+		}
+
+		client, err := mgm.NewClient(ctx, newURL.Host, key, mgmTlsEnabled)
+		if err != nil {
+			log.Infof("couldn't switch to the new Management %s", newURL.String())
+			return config, err
+		}
+		defer client.Close() //nolint
+
+		// gRPC check
+		_, err = client.GetServerPublicKey()
+		if err != nil {
+			log.Infof("couldn't switch to the new Management %s", newURL.String())
+			return nil, err
+		}
+
+		// everything is alright => update the config
+		newConfig, err := ReadConfig(newURL.String(), "", configPath, nil)
+		if err != nil {
+			log.Infof("couldn't switch to the new Management %s", newURL.String())
+			return config, fmt.Errorf("failed updating config file: %v", err)
+		}
+		log.Infof("successfully switched to the new Management URL: %s", newURL.String())
+
+		return newConfig, nil
+	}
+
+	return config, nil
+}