diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 20133fb1ae0..1cd560851c3 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -454,7 +454,7 @@ class ApplicationController < ActionController::Base
   end
 
   def can_cache_content?
-    current_user.blank? && flash[:authentication_data].blank?
+    current_user.blank? && cookies[:authentication_data].blank?
   end
 
   # Our custom cache method
diff --git a/app/controllers/users/omniauth_callbacks_controller.rb b/app/controllers/users/omniauth_callbacks_controller.rb
index ce6040816d7..65310a13c08 100644
--- a/app/controllers/users/omniauth_callbacks_controller.rb
+++ b/app/controllers/users/omniauth_callbacks_controller.rb
@@ -67,7 +67,7 @@ class Users::OmniauthCallbacksController < ApplicationController
       if (provider && provider.full_screen_login) || cookies['fsl']
         cookies.delete('fsl')
         cookies['_bypass_cache'] = true
-        flash[:authentication_data] = @auth_result.to_client_hash.to_json
+        cookies[:authentication_data] = @auth_result.to_client_hash.to_json
         redirect_to @origin
       else
         respond_to do |format|
diff --git a/app/views/layouts/application.html.erb b/app/views/layouts/application.html.erb
index 83a9b6753f7..459c778d059 100644
--- a/app/views/layouts/application.html.erb
+++ b/app/views/layouts/application.html.erb
@@ -56,8 +56,8 @@
 
     <%= tag.meta id: 'data-discourse-setup', data: client_side_setup_data %>
 
-    <%- if !current_user && flash[:authentication_data] %>
-      <meta id="data-authentication" data-authentication-data="<%= flash[:authentication_data] %>">
+    <%- if !current_user && cookies[:authentication_data] %>
+      <meta id="data-authentication" data-authentication-data="<%= cookies.delete(:authentication_data) %>">
       <%= preload_script "authentication-complete" %>
     <%- end %>
   </head>