feat: add auth middleware for protected routes

Add RequireAuth middleware that checks for a valid session and
redirects unauthenticated users to /pages/login. Applied to all
/sources and /source/{sourceID} routes. The middleware uses the
existing session package for authentication checks.

closes #9

internal/middleware/middleware.go

@@ -16,6 +16,7 @@ import (
 	"sneak.berlin/go/webhooker/internal/config"
 	"sneak.berlin/go/webhooker/internal/globals"
 	"sneak.berlin/go/webhooker/internal/logger"
+	"sneak.berlin/go/webhooker/internal/session"
 )
 
 // nolint:revive // MiddlewareParams is a standard fx naming convention
@@ -24,17 +25,20 @@ type MiddlewareParams struct {
 	Logger  *logger.Logger
 	Globals *globals.Globals
 	Config  *config.Config
+	Session *session.Session
 }
 
 type Middleware struct {
-	log    *slog.Logger
-	params *MiddlewareParams
+	log     *slog.Logger
+	params  *MiddlewareParams
+	session *session.Session
 }
 
 func New(lc fx.Lifecycle, params MiddlewareParams) (*Middleware, error) {
 	s := new(Middleware)
 	s.params = &params
 	s.log = params.Logger.Get()
+	s.session = params.Session
 	return s, nil
 }
 
@@ -118,11 +122,27 @@ func (s *Middleware) CORS() func(http.Handler) http.Handler {
 	})
 }
 
-func (s *Middleware) Auth() func(http.Handler) http.Handler {
+// RequireAuth returns middleware that checks for a valid session.
+// Unauthenticated users are redirected to the login page.
+func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			// TODO: implement proper authentication
-			s.log.Debug("AUTH: before request")
+			sess, err := s.session.Get(r)
+			if err != nil {
+				s.log.Debug("auth middleware: failed to get session", "error", err)
+				http.Redirect(w, r, "/pages/login", http.StatusSeeOther)
+				return
+			}
+
+			if !s.session.IsAuthenticated(sess) {
+				s.log.Debug("auth middleware: unauthenticated request",
+					"path", r.URL.Path,
+					"method", r.Method,
+				)
+				http.Redirect(w, r, "/pages/login", http.StatusSeeOther)
+				return
+			}
+
 			next.ServeHTTP(w, r)
 		})
 	}