caddy/caddytest/integration/caddyfile_adapt/reverse_proxy_buffers.txt

https://example.com {
	reverse_proxy https://localhost:54321 {
		request_buffers unlimited
		response_buffers unlimited
	}
}

----------
{
	"apps": {
		"http": {
			"servers": {
				"srv0": {
					"listen": [
						":443"
					],
					"routes": [
						{
							"match": [
								{
									"host": [
										"example.com"
									]
								}
							],
							"handle": [
								{
									"handler": "subroute",
									"routes": [
										{
											"handle": [
												{
													"handler": "reverse_proxy",
													"request_buffers": -1,
													"response_buffers": -1,
													"transport": {
														"protocol": "http",
														"tls": {}
													},
													"upstreams": [
														{
															"dial": "localhost:54321"
														}
													]
												}
											]
										}
									]
								}
							],
							"terminal": true
						}
					]
				}
			}
		}
	}
}