caddy/caddytest/integration/caddyfile_adapt/reverse_proxy_h2c.txt

https://example.com {
	reverse_proxy /path http://localhost:54321 {
		header_up Host {host}
		header_up X-Real-IP {remote}
		header_up X-Forwarded-For {remote}
		header_up X-Forwarded-Port {server_port}
		header_up X-Forwarded-Proto "http"
		transport http {
			versions h2c 2
			compression off
		}
	}
}

----------
{
	"apps": {
		"http": {
			"servers": {
				"srv0": {
					"listen": [
						":443"
					],
					"routes": [
						{
							"match": [
								{
									"host": [
										"example.com"
									]
								}
							],
							"handle": [
								{
									"handler": "subroute",
									"routes": [
										{
											"handle": [
												{
													"handler": "reverse_proxy",
													"headers": {
														"request": {
															"set": {
																"Host": [
																	"{http.request.host}"
																],
																"X-Forwarded-For": [
																	"{http.request.remote}"
																],
																"X-Forwarded-Port": [
																	"{server_port}"
																],
																"X-Forwarded-Proto": [
																	"http"
																],
																"X-Real-Ip": [
																	"{http.request.remote}"
																]
															}
														}
													},
													"transport": {
														"compression": false,
														"protocol": "http",
														"versions": [
															"h2c",
															"2"
														]
													},
													"upstreams": [
														{
															"dial": "localhost:54321"
														}
													]
												}
											],
											"match": [
												{
													"path": [
														"/path"
													]
												}
											]
										}
									]
								}
							],
							"terminal": true
						}
					]
				}
			}
		}
	}
}