server: Fix authentication with MySQL 5.1 and older clients

[dveeden]

What problem does this PR solve?

Issue Number: close #29725

Problem Summary:

handleAuthPlugin checks for the ClientPluginAuth capability but this didn't set the AuthPlugin causing readOptionalSSLRequestAndHandshakeResponse to return an error.

Note that this allows authentication for users that use mysql_native_password to work, but users using caching_sha2_passwords won't work.

This does now return a more specific error in case authentication with caching_sha2_password is used.

[dvaneeden@dve-carbon ~]$ ~/opt/mysql/5.1.73/bin/mysql -h 127.0.0.1 -u sha -P 4000 -psha
ERROR 1105 (HY000): ERROR 1251 (08004): Client does not support authentication protocol requested by server; consider upgrading MySQL client

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

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

None

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[dveeden]

This will need careful merging with #29577

[bb7133]

Note that this allows authentication for users that use mysql_native_password to work, but users using caching_sha2_passwords won't work.

This does now return a more specific error in case authentication with caching_sha2_password is used.

So your point is, if a user with caching_sha2_password authentication is defined, login with old MySQL client(v5.1) will not be allowed, right?

[bb7133]

Please add a test case for your change, if it can be a functional test for handleAuthPlugin() only, that would be great :)

[djshow832]

There are no such test cases in TiDB, which is the reason why there are many fix-on-a-fix problems.
Can you try to add a test case so that future modifications won't break the compatibility?

[djshow832]

Also, please add a release note so that users can figure out from the user doc that the bugfix is contained in which versions.

[djshow832]

There are no such test cases in TiDB, which is the reason why there are many fix-on-a-fix problems. Can you try to add a test case so that future modifications won't break the compatibility?

Will any authentication test cases be ported from the MySQL test? @morgo

[dveeden]

Closing this as this is now part of #29738