TUN-3449: Use flag to select transport protocol implementation

cmd/cloudflared/tunnel/cmd.go

@@ -719,6 +719,7 @@ func tunnelFlags(shouldHide bool) []cli.Flag {
 			Value:  false,
 			Hidden: shouldHide,
 		}),
+		selectProtocolFlag,
 	}...)
 
 	return flags

cmd/cloudflared/tunnel/subcommand_context.go

@@ -260,12 +260,16 @@ func (sc *subcommandContext) run(tunnelID uuid.UUID) error {
 		return err
 	}
 
+	protocol, ok := origin.ParseProtocol(sc.c.String("protocol"))
+	if !ok {
+		return fmt.Errorf("%s is not valid protocol. %s", sc.c.String("protocol"), availableProtocol)
+	}
 	return StartServer(
 		sc.c,
 		version,
 		shutdownC,
 		graceShutdownC,
-		&origin.NamedTunnelConfig{Auth: *credentials, ID: tunnelID},
+		&origin.NamedTunnelConfig{Auth: *credentials, ID: tunnelID, Protocol: protocol},
 		sc.logger,
 		sc.isUIEnabled,
 	)

cmd/cloudflared/tunnel/subcommands.go

@@ -30,6 +30,7 @@ import (
 
 const (
 	credFileFlagAlias = "cred-file"
+	availableProtocol = "Available protocols: http2, Go's implementation and h2mux, Cloudflare's implementation of HTTP/2."
 )
 
 var (
@@ -83,6 +84,13 @@ var (
 		Aliases: []string{"f"},
 		Usage:   "Allows you to delete a tunnel, even if it has active connections.",
 	}
+	selectProtocolFlag = &cli.StringFlag{
+		Name:    "protocol",
+		Value:   "h2mux",
+		Aliases: []string{"p"},
+		Usage:   fmt.Sprintf("Protocol implementation to connect with Cloudflare's edge network. %s", availableProtocol),
+		Hidden:  true,
+	}
 )
 
 func buildCreateCommand() *cli.Command {
@@ -309,6 +317,7 @@ func buildRunCommand() *cli.Command {
 	flags := []cli.Flag{
 		forceFlag,
 		credentialsFileFlag,
+		selectProtocolFlag,
 	}
 	flags = append(flags, configureProxyFlags(false)...)
 	return &cli.Command{