httpcaddyfile: Map default_bind to BindHost in globalACMEDefaults

caddyconfig/httpcaddyfile/tlsapp.go

@@ -554,6 +554,7 @@ func fillInGlobalACMEDefaults(issuer certmagic.Issuer, options map[string]any) e
 	globalPreferredChains := options["preferred_chains"]
 	globalCertLifetime := options["cert_lifetime"]
 	globalHTTPPort, globalHTTPSPort := options["http_port"], options["https_port"]
+	globalDefaultBind := options["default_bind"]
 
 	if globalEmail != nil && acmeIssuer.Email == "" {
 		acmeIssuer.Email = globalEmail.(string)
@@ -606,6 +607,20 @@ func fillInGlobalACMEDefaults(issuer certmagic.Issuer, options map[string]any) e
 		}
 		acmeIssuer.Challenges.TLSALPN.AlternatePort = globalHTTPSPort.(int)
 	}
+	// If BindHost is still unset, fall back to the first default_bind address if set
+	// This avoids binding the automation policy to the wildcard socket, which is unexpected behavior when a more selective socket is specified via default_bind
+	// In BSD it is valid to bind to the wildcard socket even though a more selective socket is already open (still unexpected behavior by the caller though)
+	// In Linux the same call will error with EADDRINUSE whenever the listener for the automation policy is opened
+	if acmeIssuer.Challenges == nil || (acmeIssuer.Challenges.DNS == nil && acmeIssuer.Challenges.BindHost == "") {
+		if defBinds, ok := globalDefaultBind.([]ConfigValue); ok && len(defBinds) > 0 {
+			if abp, ok := defBinds[0].Value.(addressesWithProtocols); ok && len(abp.addresses) > 0 {
+				if acmeIssuer.Challenges == nil {
+					acmeIssuer.Challenges = new(caddytls.ChallengesConfig)
+				}
+				acmeIssuer.Challenges.BindHost = abp.addresses[0]
+			}
+		}
+	}
 	if globalCertLifetime != nil && acmeIssuer.CertificateLifetime == 0 {
 		acmeIssuer.CertificateLifetime = globalCertLifetime.(caddy.Duration)
 	}