diff --git a/core/lib/Drupal/Core/Authentication/AuthenticationManager.php b/core/lib/Drupal/Core/Authentication/AuthenticationManager.php
index f7a9e0d..9f76338 100644
--- a/core/lib/Drupal/Core/Authentication/AuthenticationManager.php
+++ b/core/lib/Drupal/Core/Authentication/AuthenticationManager.php
@@ -114,6 +114,13 @@ public function authenticate(Request $request) {
       $this->account = drupal_anonymous_user();
     }
 
+    // No provider felt responsible – assume the one with the least priority
+    // should have.
+    if (!$this->triggeredProvider) {
+      end($this->providers);
+      $this->triggeredProvider = key($this->providers);
+    }
+
     // Set the global user to the account returned by the triggered provider.
     $user = $this->account;