lightning: when tidb.tls config set to "false", TLSConfig didn't change, and db cannot connect

[AkiraXie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. set lightning.toml security
   

2. set lightning config toml [tidb.tls] to "false"
   

3. tidb cluster open cluster tls but no client tls

2. What did you expect to see? (Required)

1. db connect ok

3. What did you see instead (Required)

1. tidb lightning encountered error: [Lightning:DB:ErrDBConnect]failed to connect database: TLS requested but server does not support TLS
2. some code shows that tlsconfig won't change
   

   tidb/pkg/lightning/config/config.go

   Lines 177 to 200 in c60f97d

   	if d.Security == nil {
   	d.Security = s
   	}
   	switch d.TLS {
   	case "skip-verify", "preferred":
   	if d.Security.TLSConfig == nil {
   	/* #nosec G402 */
   	d.Security.TLSConfig = &tls.Config{
   	MinVersion: tls.VersionTLS12,
   	InsecureSkipVerify: true,
   	NextProtos: []string{"h2", "http/1.1"}, // specify `h2` to let Go use HTTP/2.
   	}
   	d.Security.AllowFallbackToPlaintext = true
   	}
   	case "cluster":
   	if len(s.CAPath) == 0 {
   	return common.ErrInvalidConfig.GenWithStack("cannot set `tidb.tls` to 'cluster' without a [security] section")
   	}
   	case "", "false":
   	d.TLS = "false"
   	default:
   	return common.ErrInvalidConfig.GenWithStack("unsupported `tidb.tls` config %s", d.TLS)
   	}

4. What is your TiDB version? (Required)

master

[AkiraXie]

/component lightning

[lance6716]

/assign @lyzx2001

[AkiraXie]

/severity major

[lance6716]

tidb cluster open cluster tls but no client tls

Why do you expect the client can connect to TiDB cluster? https://docs.pingcap.com/zh/tidb/dev/enable-tls-between-clients-and-servers#%E9%85%8D%E7%BD%AE%E5%90%AF%E7%94%A8%E8%BA%AB%E4%BB%BD%E9%AA%8C%E8%AF%81

[AkiraXie]

tidb cluster open cluster tls but no client tls

Why do you expect the client can connect to TiDB cluster? https://docs.pingcap.com/zh/tidb/dev/enable-tls-between-clients-and-servers#%E9%85%8D%E7%BD%AE%E5%90%AF%E7%94%A8%E8%BA%AB%E4%BB%BD%E9%AA%8C%E8%AF%81

the cluster opened between-components tls but not between client-server tls , sorry for my incorrent words