Add --create-admin option

This enables automated user creation by running:

  writefreely --create-admin username:password

It will fail if an admin (first user) already exists, which makes this
suitable for use on both for single- and multi-user instances.

Closes T544

app.go

@@ -21,6 +21,7 @@ import (
 	"github.com/gorilla/sessions"
 	"github.com/manifoldco/promptui"
 	"github.com/writeas/go-strip-markdown"
+	"github.com/writeas/web-core/auth"
 	"github.com/writeas/web-core/converter"
 	"github.com/writeas/web-core/log"
 	"github.com/writeas/writefreely/config"
@@ -178,6 +179,7 @@ func Serve() {
 	doConfig := flag.Bool("config", false, "Run the configuration process")
 	genKeys := flag.Bool("gen-keys", false, "Generate encryption and authentication keys")
 	createSchema := flag.Bool("init-db", false, "Initialize app database")
+	createAdmin := flag.String("create-admin", "", "Create an admin with the given username:password")
 	resetPassUser := flag.String("reset-pass", "", "Reset the given user's password")
 	outputVersion := flag.Bool("v", false, "Output the current version")
 	flag.Parse()
@@ -281,6 +283,54 @@ func Serve() {
 			}
 		}
 		os.Exit(0)
+	} else if *createAdmin != "" {
+		// Create an admin user with --create-admin
+		creds := strings.Split(*createAdmin, ":")
+		if len(creds) != 2 {
+			log.Error("usage: writefreely --create-admin username:password")
+			os.Exit(1)
+		}
+
+		log.Info("Loading configuration...")
+		cfg, err := config.Load()
+		if err != nil {
+			log.Error("Unable to load configuration: %v", err)
+			os.Exit(1)
+		}
+		app.cfg = cfg
+		connectToDatabase(app)
+		defer shutdown(app)
+
+		// Ensure an admin / first user doesn't already exist
+		if u, _ := app.db.GetUserByID(1); u != nil {
+			log.Error("Admin user already exists (%s). Aborting.", u.Username)
+			os.Exit(1)
+		}
+
+		// Create the user
+		username := creds[0]
+		password := creds[1]
+
+		hashedPass, err := auth.HashPass([]byte(password))
+		if err != nil {
+			log.Error("Unable to hash password: %v", err)
+			os.Exit(1)
+		}
+
+		u := &User{
+			Username:   username,
+			HashedPass: hashedPass,
+			Created:    time.Now().Truncate(time.Second).UTC(),
+		}
+
+		log.Info("Creating user %s...\n", u.Username)
+		err = app.db.CreateUser(u, "")
+		if err != nil {
+			log.Error("Unable to create user: %s", err)
+			os.Exit(1)
+		}
+		log.Info("Done!")
+		os.Exit(0)
 	} else if *resetPassUser != "" {
 		// Connect to the database
 		log.Info("Loading configuration...")