By an Oracle PL/SQL, How to access a web site and retrive data from that web pages?

Hi Oracle Experts,

I am working on an Oracle PL/SQL web application, with Oracle 11.1 and Oracle HTTP server.  

I need create an Oracle procedure, to access a web site and get data from.

Any ideas?

Following is an procedure I created. Unfortunately it did not work.

ORA-29273: HTTP request failed
ORA-06512: at "SYS.UTL_HTTP", line 1130
ORA-29024: Certificate validation failure
ORA-06512: at "my_action", line 9
ORA-06512: at line 2

Procedure my_action as
 t_http_req     utl_http.req;
 t_http_resp    utl_http.resp;
 t_respond      varchar2(30000);
begin
  t_http_req:= utl_http.begin_request( 'https://www.myTargetsite.com/assignment_log')