Improve webapp sample comments and usage (#171)

samples/webappBot/index.html

@@ -24,10 +24,16 @@
 <script>
     Telegram.WebApp.ready()
 
+    // The frontend is OK displaying "unsafe" data, as long as we only use it for display reasons, and not as input.
     document.getElementById("name").innerHTML = "your name is: " + Telegram.WebApp.initDataUnsafe.user.first_name
     document.getElementById("id").innerHTML = "your id is: " + Telegram.WebApp.initDataUnsafe.user.id
 
-    fetch("{{ .WebAppURL }}/validate?" + Telegram.WebApp.initData).then(function (response) {
+    // For any input, we must always pass the initData string, which will be validated by the backend.
+    fetch("{{ .WebAppURL }}/validate", {
+        headers: {
+            "X-Auth": Telegram.WebApp.initData
+        }
+    }).then(function (response) {
         return response.text();
     }).then(function (text) {
         document.getElementById("valid").innerHTML = "result: " + text;
@@ -36,4 +42,4 @@
     });
 </script>
 </body>
-</html>
+</html>

samples/webappBot/routes.go

@@ -1,9 +1,13 @@
 package main
 
 import (
+	"encoding/json"
+	"fmt"
 	"net/http"
+	"net/url"
 	"text/template"
 
+	"github.com/PaulSonOfLars/gotgbot/v2"
 	"github.com/PaulSonOfLars/gotgbot/v2/ext"
 )
 
@@ -24,17 +28,38 @@ func index(webappURL string) func(writer http.ResponseWriter, request *http.Requ
 }
 
 func validate(token string) func(writer http.ResponseWriter, request *http.Request) {
-	return func(writer http.ResponseWriter, request *http.Request) {
-		ok, err := ext.ValidateWebAppQuery(request.URL.Query(), token)
+	return func(w http.ResponseWriter, r *http.Request) {
+		// Our index.html sends the WebApp.initData field over the X-Auth header.
+		// We parse this string as a URL query.
+		authQuery, err := url.ParseQuery(r.Header.Get("X-Auth"))
 		if err != nil {
-			writer.WriteHeader(http.StatusBadRequest)
-			writer.Write([]byte("validation failed; error: " + err.Error()))
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte("validation failed; failed to parse auth query: " + err.Error()))
+		}
+
+		// We validate that the query has been hashed correctly, ensuring data can be trusted.
+		ok, err := ext.ValidateWebAppQuery(authQuery, token)
+		if err != nil {
+			w.WriteHeader(http.StatusUnauthorized)
+			w.Write([]byte("validation failed; error: " + err.Error()))
+			return
+		}
+		if !ok {
+			w.WriteHeader(http.StatusUnauthorized)
+			w.Write([]byte("validation failed; data cannot be trusted."))
 			return
 		}
-		if ok {
-			writer.Write([]byte("validation success; user is authenticated."))
-		} else {
-			writer.Write([]byte("validation failed; data cannot be trusted."))
+
+		// Once we've confirmed the data can be trusted, we unmarshal any data we may need to use.
+		var u gotgbot.User
+		err = json.Unmarshal([]byte(authQuery.Get("user")), &u)
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte("validation failed; failed to unmarshal user: " + err.Error()))
+			return
 		}
+
+		// And then we can choose to either return it, or work with it.
+		w.Write([]byte(fmt.Sprintf("validation success; user '%s' is authenticated (id: %d).", u.FirstName, u.Id)))
 	}
 }