iRule for replacing string in HTTP POST

I am having trouble even getting started on this iRule and would love some help.

 

 

We have an application (TAM) that is sending an incorrect HTTP POST to a back end application (APEX). We need to add an additional parameter to the HTTP POST.

 

 

My HTTP Header that needs changing is currently:

 

POST /pls/htmldb/wwv_flow.accept HTTP/1.1

 

Host: oratst1:7777

 

User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1

 

Accept: text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5

 

Accept-Language: en-gb,en;q=0.5

 

Accept-Encoding: gzip,deflate

 

Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7

 

Keep-Alive: 300

 

Proxy-Connection: keep-alive

 

Referer: http://oratst1:7777/pls/htmldb/f?p=105

 

Cookie: ORACLE_PLATFORM_REMEMBER_UN=ADMIN:AMS_TST

 

Content-Type: application/x-www-form-urlencoded

 

Content-Length: 210

 

p_flow_id=105&p_flow_step_id=101&p_instance=9615267773042070588&p_page_submission_id=96363&p_request=LOGIN&p_t01=username&p_arg_names=1035622032913287&p_t02=password&p_md5_checksum=

 

 

I need the last line of the header above to actually read:

 

p_flow_id=105&p_flow_step_id=101&p_instance=9615267773042070588&p_page_submission_id=96363&p_request=LOGIN&p_arg_names=1035510424913285&p_t01=bdoadmin&p_arg_names=1035622032913287&p_t02=standard&p_md5_checksum=

 

 

The addition of "&p_arg_names=1035510424913285" is the change.

 

 

Could anyone suggest a starting point? What event to use for this?

 

 

Thank you & Kind Regards

 

Kate (kate.spath@bdo.co.uk)