vSphere UI must limit the maximum size of a POST request.
The "maxPostSize" value is the maximum size in bytes of the POST that will be handled by the container FORM URL parameter parsing. Limit its size to reduce exposure to a denial-of-service attack.
If "maxPostSize" is not set, the default value of 2097152 (2MB) is used. Security Token Service is configured in its shipping state to not set a value for "maxPostSize"'.