refactor: convert admin handlers to Gin context-based signatures

- Remove old ServeHTTP method (no longer needed with Gin routing)
- Update all 6 handler methods to use *gin.Context instead of http.ResponseWriter, *http.Request
- Convert handler signatures: handleList, handleNew, handleNewPost, handleEdit, handleDelete
- Remove render() helper (use c.HTML() directly)
- Update renderError() to accept gin.Context instead of http.ResponseWriter
- Update postFromForm() to extract form data from gin.Context using c.PostForm()
- Update main.go to use adminSrv.NewServer() and adminSrv.Engine()
- All handlers now use Gin methods: c.HTML(), c.PostForm(), c.Param(), c.Redirect()
- Path parameters now extracted via c.Param("slug") instead of function arguments
- HTTP status codes and error handling fully migrated to Gin patterns

Build verified: go build ./cmd/nebbet succeeds

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

1 files changed, 159 insertions, 0 deletions

diff --git a/internal/admin/auth/auth.go b/internal/admin/auth/auth.go
new file mode 100644
index 0000000..b0de7d9
--- /dev/null
+++ b/internal/admin/auth/auth.go
@@ -0,0 +1,159 @@
+// Package auth manages a htpasswd-compatible password file (bcrypt entries).
+// The file format is one "username:$2a$..." entry per line.
+// nginx auth_basic accepts this file directly via auth_basic_user_file.
+package auth
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+	"syscall"
+
+	"golang.org/x/crypto/bcrypt"
+	"golang.org/x/term"
+)
+
+type Auth struct {
+	path string
+}
+
+func New(path string) *Auth { return &Auth{path: path} }
+
+func (a *Auth) AddUser(username string) error {
+	users, err := a.read()
+	if err != nil && !os.IsNotExist(err) {
+		return err
+	}
+	if _, exists := users[username]; exists {
+		return fmt.Errorf("user %q already exists", username)
+	}
+	pw, err := readPassword("Password: ")
+	if err != nil {
+		return err
+	}
+	confirm, err := readPassword("Confirm:  ")
+	if err != nil {
+		return err
+	}
+	if pw != confirm {
+		return fmt.Errorf("passwords do not match")
+	}
+	hash, err := bcrypt.GenerateFromPassword([]byte(pw), bcrypt.DefaultCost)
+	if err != nil {
+		return err
+	}
+	users[username] = string(hash)
+	return a.write(users)
+}
+
+func (a *Auth) ChangePassword(username string) error {
+	users, err := a.read()
+	if err != nil {
+		return err
+	}
+	if _, exists := users[username]; !exists {
+		return fmt.Errorf("user %q not found", username)
+	}
+	pw, err := readPassword("New password: ")
+	if err != nil {
+		return err
+	}
+	confirm, err := readPassword("Confirm:      ")
+	if err != nil {
+		return err
+	}
+	if pw != confirm {
+		return fmt.Errorf("passwords do not match")
+	}
+	hash, err := bcrypt.GenerateFromPassword([]byte(pw), bcrypt.DefaultCost)
+	if err != nil {
+		return err
+	}
+	users[username] = string(hash)
+	return a.write(users)
+}
+
+func (a *Auth) DeleteUser(username string) error {
+	users, err := a.read()
+	if err != nil {
+		return err
+	}
+	if _, exists := users[username]; !exists {
+		return fmt.Errorf("user %q not found", username)
+	}
+	delete(users, username)
+	return a.write(users)
+}
+
+func (a *Auth) ListUsers() ([]string, error) {
+	users, err := a.read()
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	names := make([]string, 0, len(users))
+	for k := range users {
+		names = append(names, k)
+	}
+	return names, nil
+}
+
+func (a *Auth) Verify(username, password string) (bool, error) {
+	users, err := a.read()
+	if err != nil {
+		return false, err
+	}
+	hash, ok := users[username]
+	if !ok {
+		return false, nil
+	}
+	err = bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
+	if err == bcrypt.ErrMismatchedHashAndPassword {
+		return false, nil
+	}
+	return err == nil, err
+}
+
+func (a *Auth) read() (map[string]string, error) {
+	f, err := os.Open(a.path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	users := make(map[string]string)
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := strings.TrimSpace(scanner.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		user, hash, ok := strings.Cut(line, ":")
+		if ok {
+			users[user] = hash
+		}
+	}
+	return users, scanner.Err()
+}
+
+func (a *Auth) write(users map[string]string) error {
+	f, err := os.OpenFile(a.path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	w := bufio.NewWriter(f)
+	for user, hash := range users {
+		fmt.Fprintf(w, "%s:%s\n", user, hash)
+	}
+	return w.Flush()
+}
+
+func readPassword(prompt string) (string, error) {
+	fmt.Print(prompt)
+	b, err := term.ReadPassword(int(syscall.Stdin))
+	fmt.Println()
+	return string(b), err
+}