Support custom ssh configuration for endpoints

cmd/mutagen/forward/create.go

@@ -101,6 +101,31 @@ func createMain(_ *cobra.Command, arguments []string) error {
 		return fmt.Errorf("unable to parse destination URL: %w", err)
 	}
 
+	if source.Protocol == url.Protocol_SSH {
+		sshConfigPath := os.Getenv("MUTAGEN_SSH_CONFIG_SOURCE")
+		if sshConfigPath == "" {
+			sshConfigPath = os.Getenv("MUTAGEN_SSH_CONFIG")
+		}
+		if sshConfigPath != "" {
+			if source.Parameters == nil {
+				source.Parameters = make(map[string]string)
+			}
+			source.Parameters["ssh-config-path"] = sshConfigPath
+		}
+	}
+	if destination.Protocol == url.Protocol_SSH {
+		sshConfigPath := os.Getenv("MUTAGEN_SSH_CONFIG_DESTINATION")
+		if sshConfigPath == "" {
+			sshConfigPath = os.Getenv("MUTAGEN_SSH_CONFIG")
+		}
+		if sshConfigPath != "" {
+			if destination.Parameters == nil {
+				destination.Parameters = make(map[string]string)
+			}
+			destination.Parameters["ssh-config-path"] = sshConfigPath
+		}
+	}
+
 	// Validate the name.
 	if err := selection.EnsureNameValid(createConfiguration.name); err != nil {
 		return fmt.Errorf("invalid session name: %w", err)

cmd/mutagen/forward/list_monitor_common.go

@@ -30,6 +30,15 @@ func printEndpoint(name string, url *url.URL, configuration *forwarding.Configur
 	// Print the URL.
 	fmt.Println("\tURL:", terminal.NeutralizeControlCharacters(url.Format("\n\t\t")))
 
+	// Print parameters, if any.
+	if len(url.Parameters) > 0 {
+		fmt.Println("\tParameters:")
+		keys := selection.ExtractAndSortLabelKeys(url.Parameters)
+		for _, key := range keys {
+			fmt.Printf("\t\t%s: %s\n", key, terminal.NeutralizeControlCharacters(url.Parameters[key]))
+		}
+	}
+
 	// Print configuration information if desired.
 	if mode == common.SessionDisplayModeListLong || mode == common.SessionDisplayModeMonitorLong {
 		// Print configuration header.

cmd/mutagen/sync/create.go

@@ -109,6 +109,31 @@ func createMain(_ *cobra.Command, arguments []string) error {
 		return fmt.Errorf("unable to parse beta URL: %w", err)
 	}
 
+	if alpha.Protocol == url.Protocol_SSH {
+		sshConfigPath := os.Getenv("MUTAGEN_SSH_CONFIG_ALPHA")
+		if sshConfigPath == "" {
+			sshConfigPath = os.Getenv("MUTAGEN_SSH_CONFIG")
+		}
+		if sshConfigPath != "" {
+			if alpha.Parameters == nil {
+				alpha.Parameters = make(map[string]string)
+			}
+			alpha.Parameters["ssh-config-path"] = sshConfigPath
+		}
+	}
+	if beta.Protocol == url.Protocol_SSH {
+		sshConfigPath := os.Getenv("MUTAGEN_SSH_CONFIG_BETA")
+		if sshConfigPath == "" {
+			sshConfigPath = os.Getenv("MUTAGEN_SSH_CONFIG")
+		}
+		if sshConfigPath != "" {
+			if beta.Parameters == nil {
+				beta.Parameters = make(map[string]string)
+			}
+			beta.Parameters["ssh-config-path"] = sshConfigPath
+		}
+	}
+
 	// Validate the name.
 	if err := selection.EnsureNameValid(createConfiguration.name); err != nil {
 		return fmt.Errorf("invalid session name: %w", err)

cmd/mutagen/sync/list_monitor_common.go

@@ -90,6 +90,15 @@ func printEndpoint(name string, url *urlpkg.URL, configuration *synchronization.
 	// Print the URL.
 	fmt.Println("\tURL:", terminal.NeutralizeControlCharacters(url.Format("\n\t\t")))
 
+	// Print parameters, if any.
+	if len(url.Parameters) > 0 {
+		fmt.Println("\tParameters:")
+		keys := selection.ExtractAndSortLabelKeys(url.Parameters)
+		for _, key := range keys {
+			fmt.Printf("\t\t%s: %s\n", key, terminal.NeutralizeControlCharacters(url.Parameters[key]))
+		}
+	}
+
 	// Print configuration information if desired.
 	if mode == common.SessionDisplayModeListLong || mode == common.SessionDisplayModeMonitorLong {
 		// Print configuration header.

pkg/agent/transport/ssh/transport.go

@@ -49,15 +49,18 @@ type sshTransport struct {
 	port uint16
 	// prompter is the prompter identifier to use for prompting.
 	prompter string
+	// configPath is the path to the SSH config file to use, if specified.
+	configPath string
 }
 
 // NewTransport creates a new SSH transport using the specified parameters.
-func NewTransport(user, host string, port uint16, prompter string) (agent.Transport, error) {
+func NewTransport(user, host string, port uint16, prompter, configPath string) (agent.Transport, error) {
 	return &sshTransport{
-		user:     user,
-		host:     host,
-		port:     port,
-		prompter: prompter,
+		user:       user,
+		host:       host,
+		port:       port,
+		prompter:   prompter,
+		configPath: configPath,
 	}, nil
 }
 
@@ -95,6 +98,7 @@ func (t *sshTransport) Copy(localPath, remoteName string) error {
 
 	// Set up arguments.
 	var scpArguments []string
+	scpArguments = append(scpArguments, ssh.ConfigFlags(t.configPath)...)
 	scpArguments = append(scpArguments, ssh.CompressionFlag())
 	scpArguments = append(scpArguments, ssh.ConnectTimeoutFlag(connectTimeoutSeconds))
 	scpArguments = append(scpArguments, ssh.ServerAliveFlags(serverAliveIntervalSeconds, serverAliveCountMax)...)
@@ -155,6 +159,7 @@ func (t *sshTransport) Command(command string) (*exec.Cmd, error) {
 	// more efficient to compress at that layer, even with the slower Go
 	// implementation.
 	var sshArguments []string
+	sshArguments = append(sshArguments, ssh.ConfigFlags(t.configPath)...)
 	sshArguments = append(sshArguments, ssh.ConnectTimeoutFlag(connectTimeoutSeconds))
 	sshArguments = append(sshArguments, ssh.ServerAliveFlags(serverAliveIntervalSeconds, serverAliveCountMax)...)
 	if t.port != 0 {

pkg/forwarding/protocols/ssh/protocol.go

@@ -51,8 +51,14 @@ func (p *protocolHandler) Connect(
 		return nil, fmt.Errorf("unable to parse target specification: %w", err)
 	}
 
+	// Extract SSH config path from URL parameters if present.
+	var sshConfigPath string
+	if url.Parameters != nil {
+		sshConfigPath = url.Parameters["ssh-config-path"]
+	}
+
 	// Create an SSH agent transport.
-	transport, err := ssh.NewTransport(url.User, url.Host, uint16(url.Port), prompter)
+	transport, err := ssh.NewTransport(url.User, url.Host, uint16(url.Port), prompter, sshConfigPath)
 	if err != nil {
 		return nil, fmt.Errorf("unable to create SSH transport: %w", err)
 	}

pkg/ssh/ssh.go

@@ -49,6 +49,15 @@ func ServerAliveFlags(interval, countMax int) []string {
 	}
 }
 
+// ConfigFlags returns flags that can be passed to scp or ssh to specify a
+// custom SSH config file. Returns an empty slice if configPath is empty.
+func ConfigFlags(configPath string) []string {
+	if configPath == "" {
+		return nil
+	}
+	return []string{"-F", configPath}
+}
+
 // sshCommandPath returns the full path to use for invoking ssh. It will use the
 // MUTAGEN_SSH_PATH environment variable if provided, otherwise falling back to
 // a platform-specific implementation.

pkg/synchronization/protocols/ssh/protocol.go

@@ -44,8 +44,14 @@ func (h *protocolHandler) Connect(
 		panic("non-SSH URL dispatched to SSH protocol handler")
 	}
 
+	// Extract SSH config path from URL parameters if present.
+	var sshConfigPath string
+	if url.Parameters != nil {
+		sshConfigPath = url.Parameters["ssh-config-path"]
+	}
+
 	// Create an SSH agent transport.
-	transport, err := ssh.NewTransport(url.User, url.Host, uint16(url.Port), prompter)
+	transport, err := ssh.NewTransport(url.User, url.Host, uint16(url.Port), prompter, sshConfigPath)
 	if err != nil {
 		return nil, fmt.Errorf("unable to create SSH transport: %w", err)
 	}