FIX: Allow omniauth confirmation page to pass through GET parameters

Using the rails `form_tag` helper generates a form with the action attribute set to the current URL (without parameters). In this case, we want to include any GET parameters, so it is better to exclude the action attribute from the form tag, and allow browsers to submit to the current URL.

app/views/users/omniauth_callbacks/confirm_request.html.erb

@@ -2,9 +2,10 @@
   <h2><%= t('login.omniauth_confirm_title', provider:(t "js.login.#{params[:provider]}.name", default: params[:provider])) %></h2>
   <br/>
 
-  <%= form_tag do %>
+  <form method="post">
+    <%= hidden_field_tag :authenticity_token, form_authenticity_token %>
     <%= button_tag(type: "submit", class: "btn btn-primary") do %>
         <%= SvgSprite.raw_svg('fa-plug') %><%= t 'login.omniauth_confirm_button' %>
     <% end %>
-  <% end %>
+  </form>
 </div>