Simplexml_load_file: 401 Authorization Required

I've created a php file (getcalentries.php) that creates an xml output and have a second page (plots_test.php) that reads in the xml file and displays some plots. They've both in the same webdav folder so I have to enter authentication information to load the plotting page, but my simplexml_load_file command is failing to load: Warning: simplexml_load_file(https://www.mydomain.com/secure/getcalentries.php?id=0&start=2010-05-17&end=2010-05-31) [function.simplexml-load-file]: failed to open stream: HTTP request failed! HTTP/1.1 401 Authorization Required in /path/secure/plots_test.php on line 24 Warning: simplexml_load_file() [function.simplexml-load-file]: I/O warning : failed to load external entity "https://www.mydomain.com/secure/getcalentries.php?id=0&start=2010-05-17&end=2010-05-31" in /path/secure/plots_test.php on line 24 Feed not loading The xml file works fine because I can move it to the parent directory just above the secure folder and it will work fine. My question is how do I need to load the file so that the authentication information can get passed? I'd really prefer to keep the xml file behind the webdav folder authentication. Thanks in advance! Michael