Update app check debug provider to match other firebase sdks

To alight with other SDK's the cpp app check debug provider
will create a token on behalf of the user if they have not already
created and registered one. Users will be prompted to register token

Author: AustinBenoit

app_check/src/desktop/debug_provider_desktop.cc

@@ -15,11 +15,15 @@
 #include "app_check/src/desktop/debug_provider_desktop.h"
 
 #include <cstdint>
+#include <cstdio>
+#include <cstdlib>
 #include <map>
 #include <memory>
 #include <string>
 #include <utility>
 
+#include "app/src/uuid.h"
+
 #include "app/rest/response.h"
 #include "app/rest/transport_builder.h"
 #include "app/rest/transport_curl.h"
@@ -111,27 +115,52 @@ void DebugAppCheckProvider::GetLimitedUseToken(
   GetTokenInternal(true, completion_callback);
 }
 
+firebase::internal::Uuid  GenerateDebugToken
+
 void DebugAppCheckProvider::GetTokenInternal(
     bool limited_use,
     std::function<void(AppCheckToken, int, const std::string&)>
         completion_callback) {
-  // Identify the user's debug token
-  const char* debug_token_cstr;
-  if (!debug_token_.empty()) {
-    debug_token_cstr = debug_token_.c_str();
-  } else {
-    debug_token_cstr = std::getenv("APP_CHECK_DEBUG_TOKEN");
+  if (debug_token_.empty()) {
+    if (std::getenv("APP_CHECK_DEBUG_TOKEN")) {
+      debug_token_ = std::getenv("APP_CHECK_DEBUG_TOKEN");
+    } else {
+      // Generate UUID
+      firebase::internal::Uuid uuid;
+      uuid.Generate();
+      char uuid_str[37];
+      snprintf(uuid_str, sizeof(uuid_str),
+               "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
+               uuid.data[0], uuid.data[1], uuid.data[2], uuid.data[3],
+               uuid.data[4], uuid.data[5], uuid.data[6], uuid.data[7],
+               uuid.data[8], uuid.data[9], uuid.data[10], uuid.data[11],
+               uuid.data[12], uuid.data[13], uuid.data[14], uuid.data[15]);
+      debug_token_ = uuid_str;
+    }
   }
 
-  if (!debug_token_cstr) {
-    completion_callback({}, kAppCheckErrorInvalidConfiguration,
-                        "Missing debug token");
-    return;
+  static bool logged_token = false;
+  if (!logged_token && !debug_token_.empty()) {
+    logged_token = true;
+    std::string app_id = app_->options().app_id();
+    std::string project_id = app_->options().project_id();
+    std::string message = std::string("\nWARNING: Firebase App Check debug token: ") + debug_token_ + "\n\n" +
+                          "To use this token for app debugging, register it with your project.\n\n" +
+                          "You can do so in the Firebase Console: \n" +
+                          "https://console.firebase.google.com/project/" + project_id + "/appcheck/apps?selectedAppId=" + app_id + " \n\n" +
+                          "Or using the Firebase CLI: \n" +
+                          "firebase appcheck:debugtokens:create " + debug_token_ + " --app " + app_id + "\n\n" +
+                          "Note: To keep your project secure, please revoke and delete this token using the \n" +
+                          "Firebase Console or the CLI (`firebase appcheck:debugtokens:delete`) when you finish debugging.\n\n" +
+                          "Warning: This debug token is a secret and should not be shared or uploaded to source code.\n\n" +
+                          "Debug Token Guide: https://firebase.google.com/docs/app-check/ios/debug-provider\n" +
+                          "Firebase CLI install instructions: https://firebase.google.com/docs/cli\n";
+    firebase::LogWarning("%s", message.c_str());
   }
 
   // Exchange debug token with the backend to get a proper attestation token.
   auto request = std::make_shared<DebugTokenRequest>(app_);
-  request->SetDebugToken(debug_token_cstr);
+  request->SetDebugToken(debug_token_);
   request->SetLimitedUse(limited_use);
 
   // Use an async call, since we don't want to block on the server response.