From 9b2a812d95aa101daf9060c6d6411c59ccf08a16 Mon Sep 17 00:00:00 2001
From: Matthew Knight <mattnite@proton.me>
Date: Tue, 17 Feb 2026 15:55:34 -0800
Subject: [PATCH] Add rate limiting to authentication endpoints

Fixes #15

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 internal/handlers/public/routes.go |  9 ++--
 internal/middleware/ratelimit.go   | 86 ++++++++++++++++++++++++++++++
 2 files changed, 92 insertions(+), 3 deletions(-)
 create mode 100644 internal/middleware/ratelimit.go

diff --git a/internal/handlers/public/routes.go b/internal/handlers/public/routes.go
index 81514d6..1aa6cc7 100644
--- a/internal/handlers/public/routes.go
+++ b/internal/handlers/public/routes.go
@@ -3,6 +3,7 @@ package public
 import (
 	"net/http"
 	"strings"
+	"time"
 
 	"github.com/gin-gonic/gin"
 	"github.com/mattnite/forgejo-tickets/internal/auth"
@@ -48,6 +49,8 @@ func NewRouter(deps Dependencies) *gin.Engine {
 	ssoHandler := &SSOHandler{deps: deps}
 	r.GET("/sso/:slug", ssoHandler.HandleSSO)
 
+	authRateLimiter := middleware.NewRateLimiter(10, 1*time.Minute)
+
 	csrf := r.Group("/")
 	csrf.Use(csrfMiddleware)
 	{
@@ -56,13 +59,13 @@ func NewRouter(deps Dependencies) *gin.Engine {
 
 		authHandler := &AuthHandler{deps: deps}
 		csrf.GET("/login", authHandler.LoginForm)
-		csrf.POST("/login", authHandler.Login)
+		csrf.POST("/login", authRateLimiter.Middleware(), authHandler.Login)
 		csrf.GET("/register", authHandler.RegisterForm)
-		csrf.POST("/register", authHandler.Register)
+		csrf.POST("/register", authRateLimiter.Middleware(), authHandler.Register)
 		csrf.POST("/logout", authHandler.Logout)
 		csrf.GET("/verify-email", authHandler.VerifyEmail)
 		csrf.GET("/forgot-password", authHandler.ForgotPasswordForm)
-		csrf.POST("/forgot-password", authHandler.ForgotPassword)
+		csrf.POST("/forgot-password", authRateLimiter.Middleware(), authHandler.ForgotPassword)
 		csrf.GET("/reset-password", authHandler.ResetPasswordForm)
 		csrf.POST("/reset-password", authHandler.ResetPassword)
 
diff --git a/internal/middleware/ratelimit.go b/internal/middleware/ratelimit.go
new file mode 100644
index 0000000..da1c670
--- /dev/null
+++ b/internal/middleware/ratelimit.go
@@ -0,0 +1,86 @@
+package middleware
+
+import (
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/gin-gonic/gin"
+)
+
+type ipRecord struct {
+	mu        sync.Mutex
+	timestamps []time.Time
+}
+
+// RateLimiter holds the per-IP rate limiting state.
+type RateLimiter struct {
+	ips    sync.Map // map[string]*ipRecord
+	limit  int
+	window time.Duration
+}
+
+// NewRateLimiter creates a rate limiter that allows `limit` requests per `window` per IP.
+func NewRateLimiter(limit int, window time.Duration) *RateLimiter {
+	rl := &RateLimiter{
+		limit:  limit,
+		window: window,
+	}
+	// Periodically clean up stale entries
+	go rl.cleanup()
+	return rl
+}
+
+// cleanup removes entries that have no recent timestamps every 5 minutes.
+func (rl *RateLimiter) cleanup() {
+	ticker := time.NewTicker(5 * time.Minute)
+	for range ticker.C {
+		now := time.Now()
+		rl.ips.Range(func(key, value any) bool {
+			rec := value.(*ipRecord)
+			rec.mu.Lock()
+			if len(rec.timestamps) == 0 || now.Sub(rec.timestamps[len(rec.timestamps)-1]) > rl.window {
+				rec.mu.Unlock()
+				rl.ips.Delete(key)
+			} else {
+				rec.mu.Unlock()
+			}
+			return true
+		})
+	}
+}
+
+// Middleware returns a Gin middleware that enforces the rate limit.
+func (rl *RateLimiter) Middleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		ip := c.ClientIP()
+
+		val, _ := rl.ips.LoadOrStore(ip, &ipRecord{})
+		rec := val.(*ipRecord)
+
+		rec.mu.Lock()
+		now := time.Now()
+		cutoff := now.Add(-rl.window)
+
+		// Remove timestamps outside the sliding window
+		valid := 0
+		for _, t := range rec.timestamps {
+			if t.After(cutoff) {
+				rec.timestamps[valid] = t
+				valid++
+			}
+		}
+		rec.timestamps = rec.timestamps[:valid]
+
+		if len(rec.timestamps) >= rl.limit {
+			rec.mu.Unlock()
+			c.AbortWithStatus(http.StatusTooManyRequests)
+			return
+		}
+
+		rec.timestamps = append(rec.timestamps, now)
+		rec.mu.Unlock()
+
+		c.Next()
+	}
+}