implement a flag to specify custom crossdomain.xml (#19262)

fixes #16909

cmd/common-main.go

@@ -361,6 +361,14 @@ func buildServerCtxt(ctx *cli.Context, ctxt *serverCtxt) (err error) {
 		ctxt.ConsoleAddr = ctx.String("console-address")
 	}
 
+	if cxml := ctx.String("crossdomain-xml"); cxml != "" {
+		buf, err := os.ReadFile(cxml)
+		if err != nil {
+			return err
+		}
+		ctxt.CrossDomainXML = string(buf)
+	}
+
 	// Check "no-compat" flag from command line argument.
 	ctxt.StrictS3Compat = !(ctx.IsSet("no-compat") || ctx.GlobalIsSet("no-compat"))
 

cmd/crossdomain-xml-handler.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2015-2021 MinIO, Inc.
+// Copyright (c) 2015-2024 MinIO, Inc.
 //
 // This file is part of MinIO Object Storage stack
 //
@@ -32,10 +32,14 @@ const crossDomainXMLEntity = "/crossdomain.xml"
 // policy file that grants access to the source domain, allowing the client to continue the transaction.
 func setCrossDomainPolicyMiddleware(h http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		cxml := crossDomainXML
+		if globalServerCtxt.CrossDomainXML != "" {
+			cxml = globalServerCtxt.CrossDomainXML
+		}
 		// Look for 'crossdomain.xml' in the incoming request.
 		if r.URL.Path == crossDomainXMLEntity {
 			// Write the standard cross domain policy xml.
-			w.Write([]byte(crossDomainXML))
+			w.Write([]byte(cxml))
 			// Request completed, no need to serve to other handlers.
 			return
 		}

cmd/globals.go

@@ -171,6 +171,7 @@ type serverCtxt struct {
 	ReadHeaderTimeout   time.Duration
 	MaxIdleConnsPerHost int
 
+	CrossDomainXML string
 	// The layout of disks as interpreted
 	Layout disksLayout
 }

cmd/server-main.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2015-2023 MinIO, Inc.
+// Copyright (c) 2015-2024 MinIO, Inc.
 //
 // This file is part of MinIO Object Storage stack
 //
@@ -161,6 +161,12 @@ var ServerFlags = []cli.Flag{
 		Name:  "sftp",
 		Usage: "enable and configure an SFTP server",
 	},
+	cli.StringFlag{
+		Name:   "crossdomain-xml",
+		Usage:  "provide a custom crossdomain-xml configuration to report at http://endpoint/crossdomain.xml",
+		Hidden: true,
+		EnvVar: "MINIO_CROSSDOMAIN_XML",
+	},
 }
 
 var gatewayCmd = cli.Command{