To log the POST data (i.e. the request payload) to a log file in Apache, you can use the %{}i and %{}o variables in the LogFormat directive in the Apache HTTPD configuration file.
The %{}i variable represents the request headers, and the %{}o variable represents the response headers. By default, these variables do not include the request or response body (i.e. the POST data), but you can enable this by adding the %{}B and %{}b variables, respectively, to the LogFormat directive.
Here is an example of using the LogFormat directive to log the POST data to a log file:
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\" %{}i %{}o" combined
This directive will create a log format named combined, which includes the client's IP address, the request method, the response status code, and the request and response headers and bodies.
To use this log format, you can specify the combined log format in the CustomLog directive, as shown below:
CustomLog /path/to/log/file combined
This directive will create a log file at the specified path, and use the combined log format to log the request and response data for each request.
Keep in mind that the exact syntax and options for the LogFormat and CustomLog directives may vary depending on your specific Apache installation and configuration. It is always a good idea to refer to the official Apache documentation for detailed instructions and further information.