command/login: Fix browser launcher for WSL users

With the current implementation of terraform login, Windows Subsystem
for Linux fails to open a browser due to lack of support for xdg-open.
This commit reuses a fix from pkg/browser#8 which detects a WSL
environment and uses cmd.exe to open the URL instead.

command/webbrowser/native.go

@@ -2,6 +2,8 @@ package webbrowser
 
 import (
 	"github.com/pkg/browser"
+	"os/exec"
+	"strings"
 )
 
 // NewNativeLauncher creates and returns a Launcher that will attempt to interact
@@ -13,6 +15,18 @@ func NewNativeLauncher() Launcher {
 
 type nativeLauncher struct{}
 
+func hasProgram(name string) bool {
+	_, err := exec.LookPath(name)
+	return err == nil
+}
+
 func (l nativeLauncher) OpenURL(url string) error {
+	// Windows Subsystem for Linux (bash for Windows) doesn't have xdg-open available
+	// but you can execute cmd.exe from there; try to identify it
+	if !hasProgram("xdg-open") && hasProgram("cmd.exe") {
+		r := strings.NewReplacer("&", "^&")
+		exec.Command("cmd.exe", "/c", "start", r.Replace(url)).Run()
+	}
+
 	return browser.OpenURL(url)
 }