Forum OpenACS Q&A: Re: When using the revproxy module, how to rewrite the form
There are some servers, who have problems accepting query variables and form data at the same time (this was a problem with AOLserver). It this the problem you are facing?
Concerning rewriting the form body: everything is possible, but i would not recommend it, since you have to care for the following cases:
a) format application/x-www-form-urlencoded vs. multipart/form-data
b) content spooled to file or memory
c) updating headers (length etc.), handling transport encoding (compressed), ....
so passing the value as a query parameter is easier. If, for whatever reasons this is not possible, consider adding an extra header field.