how can I get the POST body when using apache mod_auth_form -

i'm trying use mod_auth_form using mode described in documentation "inline login body preservation". in documentation mention using mod_include or cgi errordocument in order generate login form, e.g.:

errordocument 401 /cgi-bin/login.cgi

the scenario if user wants post either non-authenticated page, or authenticated page timed-out session.

the post hits target url, intercepted mod_auth_form, invokes errordocument 401, user enters credentials. on login form page, "special" hidden form variable httpd_body can added (and httpd_method) processed authentication handler create post body original target.

the problem the login.cgi doesn't post data since (apparently) apache doesn't pass post data errordocument. alternative errordocument use directive authformloginrequiredlocation plain 302 redirect , of course post data lost.

it seems feature httpd_body impossible use, impossible capture original post data. in case of get, 1 have parse referrer get variables.

is there way in apache read post data , store somewhere before authentication hook run? or other solution i've missed?