httpcaddyfile: Map default_bind to BindHost in globalACMEDefaults

[Monviech]

Fixes: #7210

This attempts to fix issues with default_bind not being used for the tls automation policies.

In my tests with a local caddy build, I do not see the behavior described in the issue anymore.

Caddyfile for testing:

{
        http_port 8080
        https_port 8443
        default_bind ::1 127.0.0.1
        email info@example.com
}

http:// {
}

example.com {
        reverse_proxy 172.16.1.113:8000 
}

The generated json, in which we can see that challenges is now populated with ::1 (first address from default_bind):

{
	"apps": {
		"http": {
			"http_port": 8080,
			"https_port": 8443,
			"servers": {
				"srv0": {
					"listen": [
						"127.0.0.1:8080",
						"[::1]:8080"
					]
				},
				"srv1": {
					"listen": [
						"127.0.0.1:8443",
						"[::1]:8443"
					],
					"routes": [
						{
							"match": [
								{
									"host": [
										"example.com"
									]
								}
							],
							"handle": [
								{
									"handler": "subroute",
									"routes": [
										{
											"handle": [
												{
													"handler": "reverse_proxy",
													"upstreams": [
														{
															"dial": "172.16.1.113:8000"
														}
													]
												}
											]
										}
									]
								}
							],
							"terminal": true
						}
					]
				}
			}
		},
		"tls": {
			"automation": {
				"policies": [
					{
						"subjects": [
							"example.com"
						],
						"issuers": [
							{
								"challenges": {
									"bind_host": "::1",
									"http": {
										"alternate_port": 8080
									},
									"tls-alpn": {
										"alternate_port": 8443
									}
								},
								"email": "info@example.com",
								"module": "acme"
							},
							{
								"ca": "https://acme.zerossl.com/v2/DV90",
								"challenges": {
									"bind_host": "::1",
									"http": {
										"alternate_port": 8080
									},
									"tls-alpn": {
										"alternate_port": 8443
									}
								},
								"email": "info@example.com",
								"module": "acme"
							}
						]
					}
				]
			}
		}
	}
}

Assistance Disclosure

I have used ChatGPT5 Thinking to generate the code, I have authored and tested the result in a local caddy build.

I have written the code comment myself.

[CLAassistant]

All committers have signed the CLA.

[mholt]

Nice, thanks for the PR! We'll give it a try. :)