lets-go:12.2 request context for authz

snippetbox/cmd/web/context.go

@@ -0,0 +1,5 @@
+package main
+
+type contextKey string
+
+const isAuthenticatedContextKey = contextKey("isAuthenticated")

snippetbox/cmd/web/helpers.go

@@ -85,5 +85,10 @@ func (app *application) decodePostForm(r *http.Request, dst any) error {
 }
 
 func (app *application) isAuthenticated(r *http.Request) bool {
-	return app.sessionManager.Exists(r.Context(), "authenticatedUserID")
+	isAuthenticated, ok := r.Context().Value(isAuthenticatedContextKey).(bool)
+	if !ok {
+		return false
+	}
+
+	return isAuthenticated
 }

snippetbox/cmd/web/middleware.go

@@ -1,12 +1,36 @@
 package main
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 
 	"github.com/justinas/nosurf"
 )
 
+func (app *application) authenticate(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		id := app.sessionManager.GetInt(r.Context(), "authenticatedUserID")
+		if id == 0 {
+			next.ServeHTTP(w, r)
+			return
+		}
+
+		exists, err := app.users.Exists(id)
+		if err != nil {
+			app.serverError(w, r, err)
+			return
+		}
+
+		if exists {
+			ctx := context.WithValue(r.Context(), isAuthenticatedContextKey, true)
+			r = r.WithContext(ctx)
+		}
+
+		next.ServeHTTP(w, r)
+	})
+}
+
 // logRequest ...
 func (app *application) logRequest(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {

snippetbox/cmd/web/routes.go

@@ -23,7 +23,7 @@ func (app *application) routes() http.Handler {
 	fileServer := http.FileServer(http.Dir("./ui/static"))
 	router.Handler(http.MethodGet, "/static/*filepath", http.StripPrefix("/static", fileServer))
 
-	dynamic := alice.New(app.sessionManager.LoadAndSave, noSurf)
+	dynamic := alice.New(app.sessionManager.LoadAndSave, noSurf, app.authenticate)
 
 	router.Handler(http.MethodGet, "/", dynamic.ThenFunc(app.home))
 	router.Handler(http.MethodGet, "/snippet/view/:id", dynamic.ThenFunc(app.snippetView))

snippetbox/internal/models/users.go

@@ -76,5 +76,10 @@ func (m *UserModel) Authenticate(email, password string) (int, error) {
 
 // Exists
 func (m *UserModel) Exists(id int) (bool, error) {
-	return false, nil
+	var exists bool
+
+	stmt := "SELECT EXISTS(SELECT true FROM users WHERE id = ?)"
+
+	err := m.DB.QueryRow(stmt, id).Scan(&exists)
+	return exists, err
 }