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

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-7.5@b31b3e5). Click here to learn what that means.
The diff coverage is 100.0000%.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #51207   +/-   ##
================================================
  Coverage               ?   72.1356%           
================================================
  Files                  ?       1408           
  Lines                  ?     410715           
  Branches               ?          0           
================================================
  Hits                   ?     296272           
  Misses                 ?      94642           
  Partials               ?      19801           

Flag	Coverage Δ
unit	72.1356% <100.0000%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.4089% <0.0000%> (?)

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-02-21 02:25:42.981723517 +0000 UTC m=+410431.729346643: ☑️ agreed by djshow832.
• 2024-02-21 08:05:41.913070647 +0000 UTC m=+430830.660693757: ☑️ agreed by CbcWestwolf.

[easonn7]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CbcWestwolf, djshow832, easonn7

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

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [CbcWestwolf,djshow832]
• pkg/sessionctx/variable/OWNERS [easonn7]

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