The following variable substitutions are supported:

• {request}: Full HTTP request message
• {response}: Full HTTP response message
• {ts}: ISO 8601 date in GMT
• {date_iso_8601} ISO 8601 date in GMT
• {date_common_log} Apache common log date using the configured timezone.
• {host}: Host of the request
• {method}: Method of the request
• {uri}: URI of the request
• {version}: Protocol version
• {target}: Request target of the request (path + query + fragment)
• {hostname}: Hostname of the machine that sent the request
• {code}: Status code of the response (if available)
• {phrase}: Reason phrase of the response (if available)
• {error}: Any error messages (if available)
• {req_header_*}: Replace * with the lowercased name of a request header to add to the message
• {res_header_*}: Replace * with the lowercased name of a response header to add to the message
• {req_headers}: Request headers
• {res_headers}: Response headers
• {req_body}: Request body
• {res_body}: Response body