session/variable: forbid changing @@global.require_secure_transport to 'on' with SEM enabled (#47677)

[ti-chi-bot]

This is an automated cherry-pick of #47677

What problem does this PR solve?

Issue Number: close #47665

Problem Summary:

The configuration for TiDB Cloud dedicated cluster is:

require_secure_transport: OFF
ssl_ca : /var/lib/tidb-server-tls/ca.crt
ssl_cert : /var/lib/tidb-server-tls/tls.crt
ssl_key: /var/lib/tidb-server-tls/tls.key

We just provide the ca.crt file for the the users to connect the TiDB cluster. When require_secure_transport = OFF, there is no problem.

But if the user set the value of require_secure_transport to 'ON', the users can not connect to the cluster anymore!

This is because the new configuration require the mysql client to pass all ca.crt tls.crt tls.key correctly, while the user only have the ca.crt file.

What is changed and how it works?

To prevent the user from losing access of the cluster, we can forbid changing require_secure_transport system variable to 'on' as a workaround, then the user can not modify it and trigger the issue.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Modify the config.toml.example:

# Security Enhanced Mode (SEM) restricts the "SUPER" privilege and requires fine-grained privileges instead.
enable-sem = true

./bin/tidb-server -config ./pkg/config/config.toml.example
mysql -h 127.0.0.1 -u root -P 4000

mysql> set @@global.require_secure_transport = on;
ERROR 1105 (HY000): require_secure_transport can not be set to ON with SEM(security enhanced mode) enabled

• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

Forbid changing @@global.require_secure_transport variable to 'on' when SEM(security enhanced mode) is enabled

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign imtbkcat for approval. For more information see the Kubernetes Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

@ti-chi-bot: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci-tidb/build	ca923cf	link	true	/test build
idc-jenkins-ci-tidb/check_dev	ca923cf	link	true	/test check-dev
idc-jenkins-ci-tidb/unit-test	ca923cf	link	true	/test unit-test
idc-jenkins-ci-tidb/check_dev_2	ca923cf	link	true	/test check-dev2

Full PR test history. Your PR dashboard.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository. I understand the commands that are listed here.

[djshow832]

Duplicated with #48735