Add metered open signups, per-IP limits, and auth security hardening

Enables public beta signup metering: DAILY_OPEN_SIGNUPS env var controls
how many users can register without an invite code per day (0=disabled,
-1=unlimited, N=daily cap). Invite codes always bypass the limit.

Also adds per-IP signup throttling (DAILY_SIGNUPS_PER_IP, default 3/day)
and fail-closed rate limiting on auth endpoints when Redis is down.

Client dynamically fetches /api/auth/signup-info to show invite field
as optional with remaining slots when open signups are enabled.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.env.example

@@ -75,6 +75,15 @@ SECRET_KEY=
 # Enable invite-only mode (requires invitation to register)
 INVITE_ONLY=true
 
+# Metered open signups (public beta)
+# 0 = disabled (invite-only enforced), -1 = unlimited, N = max open signups per day
+# When set > 0, users can register without an invite code up to the daily limit.
+# Invite codes always work regardless of this limit.
+DAILY_OPEN_SIGNUPS=0
+
+# Max signups per IP address per day (0 = unlimited)
+DAILY_SIGNUPS_PER_IP=3
+
 # Bootstrap admin account (for first-time setup with INVITE_ONLY=true)
 # Remove these after first login!
 # BOOTSTRAP_ADMIN_USERNAME=admin

client/app.js

@@ -4762,11 +4762,14 @@ class AuthManager {
         this.signupFormContainer = document.getElementById('signup-form-container');
         this.signupForm = document.getElementById('signup-form');
         this.signupInviteCode = document.getElementById('signup-invite-code');
+        this.inviteCodeGroup = document.getElementById('invite-code-group');
+        this.inviteCodeHint = document.getElementById('invite-code-hint');
         this.signupUsername = document.getElementById('signup-username');
         this.signupEmail = document.getElementById('signup-email');
         this.signupPassword = document.getElementById('signup-password');
         this.signupError = document.getElementById('signup-error');
         this.showSignupLink = document.getElementById('show-signup');
+        this.signupInfo = null;  // populated by fetchSignupInfo()
         this.showLoginLink = document.getElementById('show-login');
         this.showForgotLink = document.getElementById('show-forgot');
         this.forgotFormContainer = document.getElementById('forgot-form-container');
@@ -4815,6 +4818,9 @@ class AuthManager {
         // Check URL for reset token or invite code on page load
         this.checkResetToken();
         this.checkInviteCode();
+
+        // Fetch signup availability info (metered open signups)
+        this.fetchSignupInfo();
     }
 
     showModal(form = 'login') {
@@ -4979,6 +4985,44 @@ class AuthManager {
         }
     }
 
+    async fetchSignupInfo() {
+        try {
+            const resp = await fetch('/api/auth/signup-info');
+            if (resp.ok) {
+                this.signupInfo = await resp.json();
+                this.updateInviteCodeField();
+            }
+        } catch (err) {
+            // Fail silently — invite field stays required by default
+        }
+    }
+
+    updateInviteCodeField() {
+        if (!this.signupInfo || !this.signupInviteCode) return;
+
+        const { invite_required, open_signups_enabled, remaining_today, unlimited } = this.signupInfo;
+
+        if (invite_required) {
+            this.signupInviteCode.required = true;
+            this.signupInviteCode.placeholder = 'Invite Code (required)';
+            if (this.inviteCodeHint) this.inviteCodeHint.textContent = '';
+        } else if (open_signups_enabled) {
+            this.signupInviteCode.required = false;
+            this.signupInviteCode.placeholder = 'Invite Code (optional)';
+            if (this.inviteCodeHint) {
+                if (unlimited) {
+                    this.inviteCodeHint.textContent = 'Open registration — no invite needed';
+                } else if (remaining_today !== null && remaining_today > 0) {
+                    this.inviteCodeHint.textContent = `${remaining_today} open signup${remaining_today !== 1 ? 's' : ''} left today`;
+                } else if (remaining_today === 0) {
+                    this.signupInviteCode.required = true;
+                    this.signupInviteCode.placeholder = 'Invite Code (required)';
+                    this.inviteCodeHint.textContent = 'Daily signups full — invite code required';
+                }
+            }
+        }
+    }
+
     async handleForgotPassword(e) {
         e.preventDefault();
         this.clearErrors();

client/index.html

@@ -893,8 +893,9 @@ TOTAL: 0 + 8 + 16 = 24 points</pre>
             <div id="signup-form-container" class="hidden">
                 <h3>Sign Up</h3>
                 <form id="signup-form">
-                    <div class="form-group">
+                    <div class="form-group" id="invite-code-group">
-                        <input type="text" id="signup-invite-code" placeholder="Invite Code" required>
+                        <input type="text" id="signup-invite-code" placeholder="Invite Code">
+                        <small id="invite-code-hint" class="form-hint"></small>
                     </div>
                     <div class="form-group">
                         <input type="text" id="signup-username" placeholder="Username" required minlength="3" maxlength="20">

client/style.css

@@ -3605,6 +3605,13 @@ input::placeholder {
     width: 100%;
 }
 
+.form-hint {
+    display: block;
+    margin-top: 4px;
+    font-size: 0.75rem;
+    color: rgba(255, 255, 255, 0.45);
+}
+
 .auth-switch {
     text-align: center;
     margin-top: 15px;

server/config.py

@@ -147,6 +147,12 @@ class ServerConfig:
     SECRET_KEY: str = ""
     INVITE_ONLY: bool = True
 
+    # Metered open signups (public beta)
+    # 0 = disabled (invite-only), -1 = unlimited, N = max per day
+    DAILY_OPEN_SIGNUPS: int = 0
+    # Max signups per IP per day (0 = unlimited)
+    DAILY_SIGNUPS_PER_IP: int = 3
+
     # Bootstrap admin (for first-time setup when INVITE_ONLY=true)
     BOOTSTRAP_ADMIN_USERNAME: str = ""
     BOOTSTRAP_ADMIN_PASSWORD: str = ""
@@ -194,6 +200,8 @@ class ServerConfig:
             ROOM_CODE_LENGTH=get_env_int("ROOM_CODE_LENGTH", 4),
             SECRET_KEY=get_env("SECRET_KEY", ""),
             INVITE_ONLY=get_env_bool("INVITE_ONLY", True),
+            DAILY_OPEN_SIGNUPS=get_env_int("DAILY_OPEN_SIGNUPS", 0),
+            DAILY_SIGNUPS_PER_IP=get_env_int("DAILY_SIGNUPS_PER_IP", 3),
             BOOTSTRAP_ADMIN_USERNAME=get_env("BOOTSTRAP_ADMIN_USERNAME", ""),
             BOOTSTRAP_ADMIN_PASSWORD=get_env("BOOTSTRAP_ADMIN_PASSWORD", ""),
             MATCHMAKING_ENABLED=get_env_bool("MATCHMAKING_ENABLED", True),

server/main.py

@@ -84,7 +84,7 @@ async def _periodic_leaderboard_refresh():
 
 
 async def _init_redis():
-    """Initialize Redis client and rate limiter."""
+    """Initialize Redis client, rate limiter, and signup limiter."""
     global _redis_client, _rate_limiter
     try:
         _redis_client = redis.from_url(config.REDIS_URL, decode_responses=False)
@@ -95,6 +95,17 @@ async def _init_redis():
             from services.ratelimit import get_rate_limiter
             _rate_limiter = await get_rate_limiter(_redis_client)
             logger.info("Rate limiter initialized")
+
+        # Initialize signup limiter for metered open signups
+        if config.DAILY_OPEN_SIGNUPS != 0 or config.DAILY_SIGNUPS_PER_IP > 0:
+            from services.ratelimit import get_signup_limiter
+            signup_limiter = await get_signup_limiter(_redis_client)
+            from routers.auth import set_signup_limiter
+            set_signup_limiter(signup_limiter)
+            logger.info(
+                f"Signup limiter initialized "
+                f"(daily={config.DAILY_OPEN_SIGNUPS}, per_ip={config.DAILY_SIGNUPS_PER_IP})"
+            )
     except Exception as e:
         logger.warning(f"Redis connection failed: {e} - rate limiting disabled")
         _redis_client = None

server/middleware/ratelimit.py

@@ -81,11 +81,15 @@ class RateLimitMiddleware(BaseHTTPMiddleware):
         # Generate client key
         client_key = self.limiter.get_client_key(request, user_id)
 
-        # Check rate limit
+        # Check rate limit (fail closed for auth endpoints)
         endpoint_key = self._get_endpoint_key(path)
         full_key = f"{endpoint_key}:{client_key}"
 
-        allowed, info = await self.limiter.is_allowed(full_key, limit, window)
+        is_auth_endpoint = path.startswith("/api/auth")
+        if is_auth_endpoint:
+            allowed, info = await self.limiter.is_allowed_strict(full_key, limit, window)
+        else:
+            allowed, info = await self.limiter.is_allowed(full_key, limit, window)
 
         # Build response
         if allowed:

server/routers/auth.py

@@ -5,6 +5,7 @@ Provides endpoints for user registration, login, password management,
 and session handling.
 """
 
+import hashlib
 import logging
 from typing import Optional
 
@@ -15,6 +16,7 @@ from config import config
 from models.user import User
 from services.auth_service import AuthService
 from services.admin_service import AdminService
+from services.ratelimit import SignupLimiter
 
 logger = logging.getLogger(__name__)
 
@@ -115,6 +117,7 @@ class SessionResponse(BaseModel):
 # These will be set by main.py during startup
 _auth_service: Optional[AuthService] = None
 _admin_service: Optional[AdminService] = None
+_signup_limiter: Optional[SignupLimiter] = None
 
 
 def set_auth_service(service: AuthService) -> None:
@@ -129,6 +132,12 @@ def set_admin_service_for_auth(service: AdminService) -> None:
     _admin_service = service
 
 
+def set_signup_limiter(limiter: SignupLimiter) -> None:
+    """Set the signup limiter instance (called from main.py)."""
+    global _signup_limiter
+    _signup_limiter = limiter
+
+
 def get_auth_service_dep() -> AuthService:
     """Dependency to get auth service."""
     if _auth_service is None:
@@ -211,15 +220,51 @@ async def register(
     auth_service: AuthService = Depends(get_auth_service_dep),
 ):
     """Register a new user account."""
-    # Validate invite code when invite-only mode is enabled
+    has_invite = bool(request_body.invite_code)
-    if config.INVITE_ONLY:
+    is_open_signup = not has_invite
-        if not request_body.invite_code:
+    client_ip = get_client_ip(request)
-            raise HTTPException(status_code=400, detail="Invite code required")
+    ip_hash = hashlib.sha256(client_ip.encode()).hexdigest()[:16] if client_ip else "unknown"
+
+    # --- Per-IP daily signup limit (applies to ALL signups) ---
+    if config.DAILY_SIGNUPS_PER_IP > 0 and _signup_limiter:
+        ip_allowed, ip_remaining = await _signup_limiter.check_ip_limit(
+            ip_hash, config.DAILY_SIGNUPS_PER_IP
+        )
+        if not ip_allowed:
+            raise HTTPException(
+                status_code=429,
+                detail="Too many signups from this address today. Please try again tomorrow.",
+            )
+
+    # --- Invite code validation ---
+    if has_invite:
         if not _admin_service:
             raise HTTPException(status_code=503, detail="Admin service not initialized")
         if not await _admin_service.validate_invite_code(request_body.invite_code):
             raise HTTPException(status_code=400, detail="Invalid or expired invite code")
+    else:
+        # No invite code — check if open signups are allowed
+        if config.INVITE_ONLY and config.DAILY_OPEN_SIGNUPS == 0:
+            raise HTTPException(status_code=400, detail="Invite code required")
 
+        # Check daily open signup limit
+        if config.DAILY_OPEN_SIGNUPS != 0 and _signup_limiter:
+            daily_allowed, daily_remaining = await _signup_limiter.check_daily_limit(
+                config.DAILY_OPEN_SIGNUPS
+            )
+            if not daily_allowed:
+                raise HTTPException(
+                    status_code=429,
+                    detail="Daily signup limit reached. Please try again tomorrow or use an invite code.",
+                )
+        elif config.DAILY_OPEN_SIGNUPS != 0 and not _signup_limiter:
+            # Signup limiter requires Redis — fail closed
+            raise HTTPException(
+                status_code=503,
+                detail="Registration temporarily unavailable. Please try again later.",
+            )
+
+    # --- Create the account ---
     result = await auth_service.register(
         username=request_body.username,
         password=request_body.password,
@@ -229,12 +274,19 @@ async def register(
     if not result.success:
         raise HTTPException(status_code=400, detail=result.error)
 
-    # Consume the invite code after successful registration
+    # --- Post-registration bookkeeping ---
-    if config.INVITE_ONLY and request_body.invite_code:
+    # Consume invite code if used
+    if has_invite and _admin_service:
         await _admin_service.use_invite_code(request_body.invite_code)
 
+    # Increment signup counters
+    if _signup_limiter:
+        if is_open_signup and config.DAILY_OPEN_SIGNUPS != 0:
+            await _signup_limiter.increment_daily()
+        if config.DAILY_SIGNUPS_PER_IP > 0:
+            await _signup_limiter.increment_ip(ip_hash)
+
     if result.requires_verification:
-        # Return user info but note they need to verify
         return {
             "user": _user_to_response(result.user),
             "token": "",
@@ -247,7 +299,7 @@ async def register(
         username=request_body.username,
         password=request_body.password,
         device_info=get_device_info(request),
-        ip_address=get_client_ip(request),
+        ip_address=client_ip,
     )
 
     if not login_result.success:
@@ -260,6 +312,32 @@ async def register(
     }
 
 
+@router.get("/signup-info")
+async def signup_info():
+    """
+    Public endpoint: returns signup availability info.
+
+    Tells the client whether invite codes are required,
+    and how many open signup slots remain today.
+    """
+    open_signups_enabled = config.DAILY_OPEN_SIGNUPS != 0
+    invite_required = config.INVITE_ONLY and not open_signups_enabled
+    unlimited = config.DAILY_OPEN_SIGNUPS < 0
+
+    remaining = None
+    if open_signups_enabled and not unlimited and _signup_limiter:
+        daily_count = await _signup_limiter.get_daily_count()
+        remaining = max(0, config.DAILY_OPEN_SIGNUPS - daily_count)
+
+    return {
+        "invite_required": invite_required,
+        "open_signups_enabled": open_signups_enabled,
+        "daily_limit": config.DAILY_OPEN_SIGNUPS if not unlimited else None,
+        "remaining_today": remaining,
+        "unlimited": unlimited,
+    }
+
+
 @router.post("/verify-email")
 async def verify_email(
     request_body: VerifyEmailRequest,

server/services/ratelimit.py

@@ -91,9 +91,42 @@ class RateLimiter:
 
         except redis.RedisError as e:
             # If Redis is unavailable, fail open (allow request)
+            # For auth-critical paths, callers should use fail_closed=True
             logger.error(f"Rate limiter Redis error: {e}")
             return True, {"remaining": limit, "reset": window_seconds, "limit": limit}
 
+    async def is_allowed_strict(
+        self,
+        key: str,
+        limit: int,
+        window_seconds: int,
+    ) -> tuple[bool, dict]:
+        """
+        Like is_allowed but fails closed (denies) when Redis is unavailable.
+        Use for security-critical paths like auth endpoints.
+        """
+        now = int(time.time())
+        window_key = f"ratelimit:{key}:{now // window_seconds}"
+
+        try:
+            async with self.redis.pipeline(transaction=True) as pipe:
+                pipe.incr(window_key)
+                pipe.expire(window_key, window_seconds + 1)
+                results = await pipe.execute()
+
+            current_count = results[0]
+            remaining = max(0, limit - current_count)
+            reset = window_seconds - (now % window_seconds)
+
+            return current_count <= limit, {
+                "remaining": remaining,
+                "reset": reset,
+                "limit": limit,
+            }
+        except redis.RedisError as e:
+            logger.error(f"Rate limiter Redis error (fail-closed): {e}")
+            return False, {"remaining": 0, "reset": window_seconds, "limit": limit}
+
     def get_client_key(
         self,
         request: Request | WebSocket,
@@ -197,8 +230,110 @@ class ConnectionMessageLimiter:
         self.timestamps = []
 
 
+class SignupLimiter:
+    """
+    Daily signup metering for public beta.
+
+    Tracks two counters in Redis:
+    - Global daily open signups (no invite code)
+    - Per-IP daily signups (with or without invite code)
+
+    Keys auto-expire after 24 hours.
+    """
+
+    def __init__(self, redis_client: redis.Redis):
+        self.redis = redis_client
+
+    def _today_key(self, prefix: str) -> str:
+        """Generate a Redis key scoped to today's date (UTC)."""
+        from datetime import datetime, timezone
+        today = datetime.now(timezone.utc).strftime("%Y-%m-%d")
+        return f"signup:{prefix}:{today}"
+
+    async def check_daily_limit(self, daily_limit: int) -> tuple[bool, int]:
+        """
+        Check if global daily open signup limit allows another registration.
+
+        Args:
+            daily_limit: Max open signups per day. -1 = unlimited, 0 = disabled.
+
+        Returns:
+            Tuple of (allowed, remaining). remaining is -1 when unlimited.
+        """
+        if daily_limit == 0:
+            return False, 0
+        if daily_limit < 0:
+            return True, -1
+
+        key = self._today_key("daily_open")
+        try:
+            count = await self.redis.get(key)
+            current = int(count) if count else 0
+            remaining = max(0, daily_limit - current)
+            return current < daily_limit, remaining
+        except redis.RedisError as e:
+            logger.error(f"Signup limiter Redis error (daily check): {e}")
+            return False, 0  # Fail closed
+
+    async def check_ip_limit(self, ip_hash: str, ip_limit: int) -> tuple[bool, int]:
+        """
+        Check if per-IP daily signup limit allows another registration.
+
+        Args:
+            ip_hash: Hashed client IP.
+            ip_limit: Max signups per IP per day. 0 = unlimited.
+
+        Returns:
+            Tuple of (allowed, remaining).
+        """
+        if ip_limit <= 0:
+            return True, -1
+
+        key = self._today_key(f"ip:{ip_hash}")
+        try:
+            count = await self.redis.get(key)
+            current = int(count) if count else 0
+            remaining = max(0, ip_limit - current)
+            return current < ip_limit, remaining
+        except redis.RedisError as e:
+            logger.error(f"Signup limiter Redis error (IP check): {e}")
+            return False, 0  # Fail closed
+
+    async def increment_daily(self) -> None:
+        """Increment the global daily open signup counter."""
+        key = self._today_key("daily_open")
+        try:
+            async with self.redis.pipeline(transaction=True) as pipe:
+                pipe.incr(key)
+                pipe.expire(key, 86400 + 60)  # 24h + 1min buffer
+                await pipe.execute()
+        except redis.RedisError as e:
+            logger.error(f"Signup limiter Redis error (daily incr): {e}")
+
+    async def increment_ip(self, ip_hash: str) -> None:
+        """Increment the per-IP daily signup counter."""
+        key = self._today_key(f"ip:{ip_hash}")
+        try:
+            async with self.redis.pipeline(transaction=True) as pipe:
+                pipe.incr(key)
+                pipe.expire(key, 86400 + 60)
+                await pipe.execute()
+        except redis.RedisError as e:
+            logger.error(f"Signup limiter Redis error (IP incr): {e}")
+
+    async def get_daily_count(self) -> int:
+        """Get current daily open signup count."""
+        key = self._today_key("daily_open")
+        try:
+            count = await self.redis.get(key)
+            return int(count) if count else 0
+        except redis.RedisError:
+            return 0
+
+
 # Global rate limiter instance
 _rate_limiter: Optional[RateLimiter] = None
+_signup_limiter: Optional[SignupLimiter] = None
 
 
 async def get_rate_limiter(redis_client: redis.Redis) -> RateLimiter:
@@ -217,7 +352,16 @@ async def get_rate_limiter(redis_client: redis.Redis) -> RateLimiter:
     return _rate_limiter
 
 
+async def get_signup_limiter(redis_client: redis.Redis) -> SignupLimiter:
+    """Get or create the global signup limiter instance."""
+    global _signup_limiter
+    if _signup_limiter is None:
+        _signup_limiter = SignupLimiter(redis_client)
+    return _signup_limiter
+
+
 def close_rate_limiter():
     """Close the global rate limiter."""
-    global _rate_limiter
+    global _rate_limiter, _signup_limiter
     _rate_limiter = None
+    _signup_limiter = None