Error 500 Internal Server Error when trying to access a service

Usually, you try to access this SP, sometimes you're successful, other times you've failed. Trying to press "enter" on the URL sometimes get you through, if you're lucky...

When you go to the SP log, you won't see anything strange. In fact, all the SP logs say wonderful things about how it receives the attributes etc etc.

Checking mod_jk log or apache log will reveal more info. It simply says

[error] serialize.request() Error serializing header value
[error] ajp13.service(): error marshaling
[error] lb.service() worker failed 120000 for ajp13:localhost:8009
[error] lb.service() unrecoverable error...
[error] mod_jk2.handler() Error connecting to tomcat 120000, status 0

Which indicates that mod_jk somewhat has failed to talk to your nice application.

This error just indicates that mod_jk has failed to transfer all header values to tomcat cause they are too large to pass through the pipe.

If you check you vhost config for the application, you'd notice that you must have used ShibExportAssertion On to protect your application. This has forced shib SP to send raw assertion to the application, which unfortunately could be very large and will fill up mod_jk buffer.

Unless you really need the raw assertion, you can safely remove that option and making your application works perfectly fine. The raw assertion is available for your application to parse manually. The data of the assertion is available as headers, which most of the case would be sufficient for the application to make authZ decision.