Identified by "nou nou" in https://www.phpbb.com/community/viewtopic.php?f=64&t=2510671#p15248641

The ucp_login_link.html template in phpBB 3.2.7 proSilver consume the existing {S_LOGIN_REDIRECT} (so should not be broken in phpBB 3.2.7), but in shipping phpBB 3.2.7 proSilver has not been updated to also consume {S_FORM_TOKEN_LOGIN}.

I do not know how to setup the needed external login dependency to create the association that would actually invoke this type of login.  But it seemed reasonable that this template needs to be updated same as all the other templates containing login forms.