Post Preservation Data leads to a 413 HTTP Error Request entity too large

Document ID : KB000117171
Last Modified Date : 09/10/2018
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Issue:
When using the Cookie Provider and a POST Form in a Siteminder protected page the Post Preservation Data is stored in a GET Parameter: 

sample: 
https://cp.abc.com/SmMakeCookie.ccc?SMSESSION=-SM-EAPqiHqNo5pRDf2669IneSkhYSlVhjX2pxD%2fYhZ0VNV%2fgPPZ8w9uk6eVGwtxLoVCxJK7MlgAbgONnRIBXb%2fyQLCtEFba0iwEEfz9%2bhFTyNCrvEetbiIJzZ6l2CkI4h5h2lvw9a83yWabvp16Hh4who9f8Vz7IgaL%2f2FCxkuI31ItYa57IzU8X8lp0Vef4Io%2baUCHDrD%2b284VSzdIhz3KuxCMuyFiRTtreIUHdpAnSTnemmMiVZqN5XqwQQdp9G8EpqrhLZ4PTpC94WvpbKvMdtEICihO79SoBFfxV2zcdJLfdqB%2fZqi4PWXl7UgiNzBJ4bn3NGVL6mCoHWeqvm%2fq5bSnOUxfHP26xhpx7tZci3A9PHBPg98xp9258gKS1pwRuNWJpTOHVcgPj%2f1eZVU3wxq%2ffzu4zXaZ3x20QnR307vXYMN9TdrwdrNvJrQmWPJM2XPbulMSZPFSSQwFMLFPWnZ3EKDFRKVo%2fggDYsldLoMtkPhfx6swUPUB9KrMqMj8zkbp61YI5yLfM%2b1HOL%2fjnSbMq1ZL0Ie5wOK2lSqUf2BXrT%2bsbXHe3%2f%2ftA2drPaK2wC0m%2f6ANOWrCg1yt9QZ9%2bRj3utq4kUMgtYBjv3WjFP66x7r4pCv9ZkwfAmCGWNWFz%2blggXeXLByHiOJX5sP36UNKzYnrFKVFrsOP8Wk%2f47qfoy%2fSv1f%2fdfknA0ib5oexm%2bJ1mh68tBuKzVAClmJCoobY%2bJLdRHf%2fktsW0XV%2bjlfa9T3aEUhvf8fyWf1oGzP8gIGG8FqsmwOsdnWF6UWSULCbo9MnQ4bpNdBY%2b3bZFWTsNOsXAK0DMB4oCydlrM1Vngfa0687xyLeegOOQmtwTf1WiU7ZkzHJ%2blTzLs5IOfVmApLrGF7%2fkpwf3c8dMAy0FA%2fcTCeNhwyjoWLAgP5hUv2VGp38TX8r4ch2twbRTR5GCvs1DkAVm6zppFX7BX2QKNlqrYyASXU1OsZaW1P5%2bP1trxEhCf6bQ7LrwMV%2fDLOSYM4aN61JMRgvtOVOaqcGOV%2f%2f6bFP47JeFZMTy4WdTvRkv3pqwbyjV8JQ6oIgUgnKB7SKne9kZ4wqGW0YV%2bAho0lpntrhsls6PO%2bkrffaMIFb%2f3lMODa2ryvw%2bh6TqiHsPcSq7sAZq5M8BGErqKkyiYoP4UWilFryH17ORTc0gmukAPchPN2SLQMB9trJMQxaK4tOqmikgcQdeyjkCRVksBwaw7cFwRp0hI6ZiD8L%2b2QSaCsDp8aQpnePNGl%2bCsN5Ro8tHZZFPPunqNIytGA0N7YaY%2bph%2bbBQk4xwwUb6ZWp0IS%2fK7U0Zfjg3NVcGGmIw79sqYddIYyhyMnE3pycRrRavPEF04mp0ppB4Ldvneii71p9v92LI&PERSIST=0&TARGET=-SM-HTTPS[...]FormSubmitListener--content~area--page~width--column--1--component--container--component--2--container--component--1--contactform--form 

In our case, it leads to a 413 HTTP Error Request entity too large. 

The size of the POST data is not predictable and so simply setting the request entity value higher is not a good solution for us.

Is there any option to prevent this behaviour?  
 
Environment:
Policy server 12.52.X
Resolution:
If you do not need to use POST preservation, you can disable it with the following parameter: 

PreservePostData 

Specifies whether the Web Agent preserves POST data when redirecting requests. When the user is challenged for advanced authentication, such as forms or certificate authentication, the post data is preserved during the authentication phase. 

Default: Yes 

To disable POST preservation, set the value of the PreservePostData parameter to no. 

https://docops.ca.com/ca-single-sign-on/12-52-sp1/en/configuring/web-agent-configuration/forms-authentication/how-to-configure-an-agent-to-support-html-forms-authentication/configure-post-preservation