server: handle clients without authplugin support (#27931)

[ti-srebot]

cherry-pick #27931 to release-5.2
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/28734

After apply modifications, you can push your change to this PR via:

git push [email protected]:ti-srebot/tidb.git pr/28734:release-5.2-fd42198c3916

---

What problem does this PR solve?

Issue Number: close #27855

Problem Summary:

Old (MySQL 5.1 and before) clients that don't send authentication plugin info in the login packet were having issues authenticating and/or got an incorrect error message

What is changed and how it works?

1. The code now checks for mysql.ClientPluginAuth in resp.Capability.
2. Instead of returning an error it now logs a warning if it encounters an unknown authentication plugin

Check List

Tests

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

Documentation

• Affects user behaviors
• Changes MySQL compatibility

Release note

Fixed a bug where MySQL 5.1 and older clients had issues authenticating

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• dveeden
• morgo

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

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

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[ti-srebot]

/run-all-tests

[ti-srebot]

@dveeden you're already a collaborator in bot's repo.

[morgo]

/run-check_dev

[morgo]

@dveeden The test failures are caused by us porting tests in master to testify, but release-5.2 uses testkit:

[2021-10-11T16:26:43.588Z] server/conn_test.go:883:30: undeclared name: `testing` (typecheck)

[2021-10-11T16:26:43.588Z] func TestHandleAuthPlugin(t *testing.T) {

[2021-10-11T16:26:43.588Z]                              ^

[2021-10-11T16:26:43.588Z] server/conn_test.go:886:26: CreateMockStore not declared by package testkit (typecheck)

[2021-10-11T16:26:43.588Z] 	store, clean := testkit.CreateMockStore(t)

[2021-10-11T16:26:43.588Z] 	                        ^

[2021-10-11T16:26:43.588Z] server/conn_test.go:894:2: undeclared name: `require` (typecheck)

[2021-10-11T16:26:43.588Z] 	require.NoError(t, err)

[2021-10-11T16:26:43.588Z] 	^

[2021-10-11T16:26:43.588Z] server/conn_test.go:909:2: undeclared name: `require` (typecheck)

[2021-10-11T16:26:43.588Z] 	require.NoError(t, err)

[2021-10-11T16:26:43.588Z] 	^

[2021-10-11T16:26:43.588Z] server/conn_test.go:913:2: undeclared name: `require` (typecheck)

[2021-10-11T16:26:43.588Z] 	require.NoError(t, err)

[2021-10-11T16:26:43.588Z] 	^

[2021-10-11T16:26:43.588Z] level=info msg="File cache stats: 1161 entries of total size 19.4MiB"

[2021-10-11T16:26:43.588Z] level=info msg="Memory: 493 samples, avg is 3425.9MB, max is 6689.3MB"

[2021-10-11T16:26:43.588Z] level=info msg="Execution took 50.474166118s"

[zimulala]

@dveeden Please address the comment.

[dveeden]

/assign @morgo @tiancaiamao

[zhouqiang-cl]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: afddb6a

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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 ti-community-infra/tichi repository.