v5.2.0 version, auto-tls default value is ture in config.toml.example but false in online tidb

[seiya-annie]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

in config.toml.example
Automatic creation of TLS certificates.
Setting it to 'true' is recommended because it is safer and tie with the default configuration of MySQL.
If this config is commented/missed, the value would be 'false' for the compatibility with TiDB versions that does not support it.
auto-tls = true

in tidb instance:
select @@tidb_config\G;
"security": {
"skip-grant-table": false,
"ssl-ca": "",
"ssl-cert": "",
"ssl-key": "",
"require-secure-transport": false,
"cluster-ssl-ca": "",
"cluster-ssl-cert": "",
"cluster-ssl-key": "",
"cluster-verify-cn": null,
"spilled-file-encryption-method": "plaintext",
"enable-sem": false,
"auto-tls": false

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

default value should be same

3. What did you see instead (Required)

different

4. What is your TiDB version? (Required)

| Release Version: v5.2.0
Edition: Community
Git Commit Hash: 3b39fed
Git Branch: heads/refs/tags/v5.2.0
UTC Build Time: 2021-08-26 05:50:13
GoVersion: go1.16.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false |

[dveeden]

This is related to #27486
cc @bb7133

[seiya-annie]

The problem here is, many of the users may not be aware if they're using a client with the encrypted connection, so we decided to set the default value of auto_tls in the code to avoid the potential performance regression while keeping it to true in the config example file.

However, the value in the config example file will be kept to true so that it is recommended(mostly for new clusters).

[ti-srebot]

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