Make people visit the log in page for mellon IAP

You can't POST login/password to the mellon login page like
the log in modal does, you have to visit the page.

Co-authored-by: Adrian Schröter <adrian@suse.de>

src/api/app/helpers/webui/webui_helper.rb

@@ -292,7 +292,11 @@ def sign_up_link(css_class: nil)
   end
 
   def log_in_link(css_class: nil)
-    if kerberos_mode?
+    if CONFIG['proxy_auth_mode'] == :mellon
+      link_to(CONFIG['proxy_auth_login_page'], class: css_class) do
+        link_content('Log In', css_class, 'fa-sign-in-alt')
+      end
+    elsif kerberos_mode?
       link_to(new_session_path, class: css_class) do
         link_content('Log In', css_class, 'fa-sign-in-alt')
       end