Add password complexity requirements

Require at least one uppercase letter, one lowercase letter, and one
digit in addition to the existing 8-character minimum.

Fixes #31
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/handlers/public/auth.go

@@ -4,6 +4,7 @@ import (
 	"net/http"
 	"net/url"
 	"strings"
+	"unicode"
 
 	"github.com/gin-gonic/gin"
 	"github.com/mattnite/forgejo-tickets/internal/auth"
@@ -11,6 +12,28 @@ import (
 	"github.com/rs/zerolog/log"
 )
 
+// validatePassword checks password complexity requirements.
+func validatePassword(password string) string {
+	if len(password) < 8 {
+		return "Password must be at least 8 characters"
+	}
+	var hasUpper, hasLower, hasDigit bool
+	for _, r := range password {
+		switch {
+		case unicode.IsUpper(r):
+			hasUpper = true
+		case unicode.IsLower(r):
+			hasLower = true
+		case unicode.IsDigit(r):
+			hasDigit = true
+		}
+	}
+	if !hasUpper || !hasLower || !hasDigit {
+		return "Password must contain at least one uppercase letter, one lowercase letter, and one digit"
+	}
+	return ""
+}
+
 type AuthHandler struct {
 	deps Dependencies
 }
@@ -85,8 +108,8 @@ func (h *AuthHandler) Register(c *gin.Context) {
 		return
 	}
 
-	if len(password) < 8 {
+	if errMsg := validatePassword(password); errMsg != "" {
-		data["Error"] = "Password must be at least 8 characters"
+		data["Error"] = errMsg
 		h.deps.Renderer.Render(c.Writer, c.Request, "register", data)
 		return
 	}
@@ -189,10 +212,10 @@ func (h *AuthHandler) ResetPassword(c *gin.Context) {
 		return
 	}
 
-	if len(password) < 8 {
+	if errMsg := validatePassword(password); errMsg != "" {
 		h.deps.Renderer.Render(c.Writer, c.Request, "reset-password", map[string]interface{}{
 			"Token": token,
-			"Error": "Password must be at least 8 characters",
+			"Error": errMsg,
 		})
 		return
 	}