(logging) {
	log {
		output file /var/log/caddy/{args[0]}.access.log
	}
}

a.example.com {
	import logging a.example.com
}

b.example.com {
	import logging b.example.com
}
----------
{
	"logging": {
		"logs": {
			"default": {
				"exclude": [
					"http.log.access.log0",
					"http.log.access.log1"
				]
			},
			"log0": {
				"writer": {
					"filename": "/var/log/caddy/a.example.com.access.log",
					"output": "file"
				},
				"include": [
					"http.log.access.log0"
				]
			},
			"log1": {
				"writer": {
					"filename": "/var/log/caddy/b.example.com.access.log",
					"output": "file"
				},
				"include": [
					"http.log.access.log1"
				]
			}
		}
	},
	"apps": {
		"http": {
			"servers": {
				"srv0": {
					"listen": [
						":443"
					],
					"routes": [
						{
							"match": [
								{
									"host": [
										"a.example.com"
									]
								}
							],
							"terminal": true
						},
						{
							"match": [
								{
									"host": [
										"b.example.com"
									]
								}
							],
							"terminal": true
						}
					],
					"logs": {
						"logger_names": {
							"a.example.com": "log0",
							"b.example.com": "log1"
						}
					}
				}
			}
		}
	}
}