ferrum/internal/auth/auth.go

// Package auth implements local username/password auth with bcrypt hashing
// and server-side sessions backed by an HTTP-only cookie.
package auth

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"net/http"
	"time"

	"github.com/google/uuid"
	"golang.org/x/crypto/bcrypt"

	"ferrum/internal/store"
)

const (
	SessionCookieName = "ferrum_session"
	sessionTTL        = 30 * 24 * time.Hour
)

var (
	ErrInvalidCredentials  = errors.New("invalid username or password")
	ErrAlreadyBootstrapped = errors.New("an admin user already exists")
)

type User struct {
	ID          string `json:"id"`
	Username    string `json:"username"`
	Email       string `json:"email"`
	IsAdmin     bool   `json:"isAdmin"`
	TOTPEnabled bool   `json:"totpEnabled"`
}

type Service struct {
	db *store.DB
}

func NewService(db *store.DB) *Service {
	return &Service{db: db}
}

// NeedsSetup reports whether no user exists yet, meaning the frontend should
// show the first-run setup wizard instead of the login page.
func (s *Service) NeedsSetup(ctx context.Context) (bool, error) {
	var count int
	if err := s.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM users`).Scan(&count); err != nil {
		return false, err
	}
	return count == 0, nil
}

// Bootstrap creates the first admin user. It refuses to run if any user already exists.
func (s *Service) Bootstrap(ctx context.Context, username, email, password string) (*User, error) {
	needsSetup, err := s.NeedsSetup(ctx)
	if err != nil {
		return nil, err
	}
	if !needsSetup {
		return nil, ErrAlreadyBootstrapped
	}
	return s.createUser(ctx, username, email, password, true)
}

func (s *Service) createUser(ctx context.Context, username, email, password string, isAdmin bool) (*User, error) {
	hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)
	if err != nil {
		return nil, err
	}
	id := uuid.NewString()
	now := time.Now().UTC().Format(time.RFC3339)
	if _, err := s.db.ExecContext(ctx,
		`INSERT INTO users (id, username, email, password_hash, is_admin, created_at, updated_at) VALUES (?, ?, ?, ?, ?, ?, ?)`,
		id, username, email, string(hash), boolToInt(isAdmin), now, now,
	); err != nil {
		return nil, err
	}
	return &User{ID: id, Username: username, Email: email, IsAdmin: isAdmin}, nil
}

// VerifyPassword checks username/password and returns the matching user
// without creating a session — the caller decides whether a second TOTP
// step is required (User.TOTPEnabled) before calling CreateSession.
// dummyBcryptHash is compared against when the username doesn't exist so
// "unknown user" and "wrong password" take the same time — otherwise the
// missing bcrypt pass leaks valid usernames through response timing.
var dummyBcryptHash = func() []byte {
	// bcrypt hash of a random never-used password
	return []byte("$2a$10$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdL17lhWy")
}()

func (s *Service) VerifyPassword(ctx context.Context, username, password string) (*User, error) {
	var (
		id, uname, email, hash string
		isAdmin, totpEnabled   int
	)
	err := s.db.QueryRowContext(ctx,
		`SELECT id, username, email, password_hash, is_admin, totp_enabled FROM users WHERE username = ?`,
		username,
	).Scan(&id, &uname, &email, &hash, &isAdmin, &totpEnabled)
	if err != nil {
		// Spend the same bcrypt work a real user lookup would, then fail.
		_ = bcrypt.CompareHashAndPassword(dummyBcryptHash, []byte(password))
		return nil, ErrInvalidCredentials
	}
	if bcrypt.CompareHashAndPassword([]byte(hash), []byte(password)) != nil {
		return nil, ErrInvalidCredentials
	}
	return &User{ID: id, Username: uname, Email: email, IsAdmin: isAdmin == 1, TOTPEnabled: totpEnabled == 1}, nil
}

// FindOrCreateOIDCUser resolves a verified OIDC identity to a local user:
// an existing user already linked to this subject, an existing local user
// with the same email (linked on first SSO login), or — failing both — a
// newly provisioned account. New OIDC accounts are never admins; promote
// them from the Users page like any other account. They get a random,
// never-disclosed password hash so the (unused) password login path stays
// closed for them, without needing a schema change to make password_hash
// nullable.
//
// emailVerified gates the risky paths: an unverified email address is never
// used to link into (or name-collide with) an existing account, because a
// hostile IdP account claiming someone else's address would otherwise take
// that account over. Unverified users get a placeholder email instead.
func (s *Service) FindOrCreateOIDCUser(ctx context.Context, subject, email, preferredUsername string, emailVerified bool) (*User, error) {
	var (
		id, uname, mail      string
		isAdmin, totpEnabled int
	)
	err := s.db.QueryRowContext(ctx,
		`SELECT id, username, email, is_admin, totp_enabled FROM users WHERE oidc_subject = ?`, subject,
	).Scan(&id, &uname, &mail, &isAdmin, &totpEnabled)
	if err == nil {
		return &User{ID: id, Username: uname, Email: mail, IsAdmin: isAdmin == 1, TOTPEnabled: totpEnabled == 1}, nil
	}

	if email != "" && emailVerified {
		err = s.db.QueryRowContext(ctx,
			`SELECT id, username, email, is_admin, totp_enabled FROM users WHERE email = ?`, email,
		).Scan(&id, &uname, &mail, &isAdmin, &totpEnabled)
		if err == nil {
			if _, err := s.db.ExecContext(ctx, `UPDATE users SET oidc_subject = ? WHERE id = ?`, subject, id); err != nil {
				return nil, err
			}
			return &User{ID: id, Username: uname, Email: mail, IsAdmin: isAdmin == 1, TOTPEnabled: totpEnabled == 1}, nil
		}
	} else if email != "" {
		// A local account already holds this (unverified) address: refuse
		// rather than silently creating a second user for the same email.
		var exists int
		if err := s.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM users WHERE email = ?`, email).Scan(&exists); err == nil && exists > 0 {
			return nil, fmt.Errorf("SSO account email is not verified by the provider and collides with an existing local account")
		}
	}

	username := preferredUsername
	if username == "" {
		username = email
	}
	if username == "" {
		username = "sso-" + subject
	}
	username = s.uniqueUsername(ctx, username)
	if email == "" || !emailVerified {
		// users.email is NOT NULL UNIQUE; synthesize a placeholder that can't collide.
		email = username + "@sso.local"
	}

	randomPassword := make([]byte, 32)
	if _, err := rand.Read(randomPassword); err != nil {
		return nil, err
	}
	hash, err := bcrypt.GenerateFromPassword(randomPassword, bcrypt.DefaultCost)
	if err != nil {
		return nil, err
	}

	id = uuid.NewString()
	now := time.Now().UTC().Format(time.RFC3339)
	if _, err := s.db.ExecContext(ctx,
		`INSERT INTO users (id, username, email, password_hash, is_admin, oidc_subject, created_at, updated_at) VALUES (?, ?, ?, ?, 0, ?, ?, ?)`,
		id, username, email, string(hash), subject, now, now,
	); err != nil {
		return nil, err
	}
	return &User{ID: id, Username: username, Email: email, IsAdmin: false}, nil
}

func (s *Service) uniqueUsername(ctx context.Context, base string) string {
	candidate := base
	for i := 2; i < 100; i++ {
		var exists int
		_ = s.db.QueryRowContext(ctx, `SELECT COUNT(*) FROM users WHERE username = ?`, candidate).Scan(&exists)
		if exists == 0 {
			return candidate
		}
		candidate = fmt.Sprintf("%s-%d", base, i)
	}
	return base + "-" + uuid.NewString()[:8]
}

// Login verifies credentials and, on success, creates a new session and
// returns the session token to be set as a cookie. It is a convenience
// wrapper for the common case (no TOTP) — see VerifyPassword + CreateSession
// for the two-step flow used when TOTP is enabled.
func (s *Service) Login(ctx context.Context, username, password string) (*User, string, error) {
	user, err := s.VerifyPassword(ctx, username, password)
	if err != nil {
		return nil, "", err
	}
	token, err := s.CreateSession(ctx, user.ID)
	if err != nil {
		return nil, "", err
	}
	return user, token, nil
}

// CreateSession mints a new session for an already-authenticated user.
// Opportunistically purges expired rows so the table doesn't grow forever.
func (s *Service) CreateSession(ctx context.Context, userID string) (string, error) {
	token := randomToken()
	now := time.Now().UTC()
	if _, err := s.db.ExecContext(ctx,
		`INSERT INTO sessions (id, user_id, token_hash, created_at, expires_at) VALUES (?, ?, ?, ?, ?)`,
		uuid.NewString(), userID, hashToken(token), now.Format(time.RFC3339), now.Add(sessionTTL).Format(time.RFC3339),
	); err != nil {
		return "", err
	}
	_, _ = s.db.ExecContext(ctx, `DELETE FROM sessions WHERE expires_at < ?`, now.Format(time.RFC3339))
	return token, nil
}

// Authenticate resolves a session cookie value into the user that owns it.
func (s *Service) Authenticate(ctx context.Context, token string) (*User, error) {
	if token == "" {
		return nil, ErrInvalidCredentials
	}
	var (
		id, username, email  string
		isAdmin, totpEnabled int
		expiresAt            string
	)
	err := s.db.QueryRowContext(ctx, `
		SELECT u.id, u.username, u.email, u.is_admin, u.totp_enabled, s.expires_at
		FROM sessions s JOIN users u ON u.id = s.user_id
		WHERE s.token_hash = ?`, hashToken(token),
	).Scan(&id, &username, &email, &isAdmin, &totpEnabled, &expiresAt)
	if err != nil {
		return nil, ErrInvalidCredentials
	}
	expiry, err := time.Parse(time.RFC3339, expiresAt)
	if err != nil || time.Now().UTC().After(expiry) {
		// Expired (or corrupt) session — drop it so the row can't accumulate.
		_, _ = s.db.ExecContext(ctx, `DELETE FROM sessions WHERE token_hash = ?`, hashToken(token))
		return nil, ErrInvalidCredentials
	}
	return &User{ID: id, Username: username, Email: email, IsAdmin: isAdmin == 1, TOTPEnabled: totpEnabled == 1}, nil
}

// Logout revokes the session associated with the given token.
func (s *Service) Logout(ctx context.Context, token string) error {
	_, err := s.db.ExecContext(ctx, `DELETE FROM sessions WHERE token_hash = ?`, hashToken(token))
	return err
}

func randomToken() string {
	b := make([]byte, 32)
	_, _ = rand.Read(b)
	return hex.EncodeToString(b)
}

func hashToken(token string) string {
	sum := sha256.Sum256([]byte(token))
	return hex.EncodeToString(sum[:])
}

func boolToInt(b bool) int {
	if b {
		return 1
	}
	return 0
}

// SetSessionCookie writes the session cookie on the response.
func SetSessionCookie(w http.ResponseWriter, token string, secure bool) {
	http.SetCookie(w, &http.Cookie{
		Name:     SessionCookieName,
		Value:    token,
		Path:     "/",
		HttpOnly: true,
		Secure:   secure,
		SameSite: http.SameSiteLaxMode,
		Expires:  time.Now().Add(sessionTTL),
	})
}

// ClearSessionCookie expires the session cookie on the response.
func ClearSessionCookie(w http.ResponseWriter, secure bool) {
	http.SetCookie(w, &http.Cookie{
		Name:     SessionCookieName,
		Value:    "",
		Path:     "/",
		HttpOnly: true,
		Secure:   secure,
		SameSite: http.SameSiteLaxMode,
		MaxAge:   -1,
	})
}