I understand that configured attributes will be stored as environment variables by default and will be accessible like
request.getAttribute(\"Shib-Identity-P
Make sure you have this field in you attribute map file.
1.1 And idP has to send the attribute too.
Since you have attribute prefix as "AJP_" your attributes will be coming as "AJP_attributeName" (This can vary too)
2.1 You have to open up your AJP port which usually listens on 8009 and redirect the /secure path to AJP. You have to do this in apache to forward proxy as AJP.
2.2 In your servlet/handler of /secure path try getting attribute as request.getHeader("AJP_attrName").
(Can try following too if this does not work a. reqest.getAttribute("attr") b. reqest.getAttribute("AJP_attr") c. header.getAttribute("attr") c. header.getAttribute("AJP_attr"). I am telling you to try out this because I have done this long time ago and I am not sure about exact method.)