*: Fix use of user identity in SHOW GRANTS + error messages

[morgo]

What problem does this PR solve?

Issue Number: fixes #30279 (once new tidb-test PR merged as well)

Problem Summary:

#30204 revealed a bug (i.e. it's not specifically a regression introduced) where the column used in show grants is from the Hostname of the user that logged in, not the matching entry from the MySQL privileges table.

Upon further inspection, it looks like we almost always intend to use the user from the privileges table and not the hostname of the logged in user. The exception is the USER() sql function.

(MySQL is actually inconsistent in which hostname it uses in error messages. The important case is with SHOW GRANTS FOR CURRENT_USER() which is used in integration tests.)

What is changed and how it works?

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

TiDB now more consistently prints the user+hostname of a user in error messages.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• dveeden
• tiancaiamao

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.

[morgo]

/run-integration-tests tidb-test=pr/1383

[morgo]

/run-integration-test --tidb-test=pr/1383

[dveeden]

Manually testing this with v5.3.0 and master @ 13d0deb show the same error messages as in this test. Are you sure this test fails without your fix?

[dvaneeden@dve-carbon ~]$ mysqlsh mysql://root@127.0.0.1:4000

sql> SHOW CREATE USER 'specifichost'@'192.168.1.54'\G
*************************** 1. row ***************************
CREATE USER for specifichost@192.168.1.54: CREATE USER 'specifichost'@'192.168.1.54' IDENTIFIED WITH 'mysql_native_password' AS '' REQUIRE NONE PASSWORD EXPIRE DEFAULT ACCOUNT UNLOCK
1 row in set (0.0015 sec)

sql> SHOW CREATE USER 'wildcard'@'%'\G
*************************** 1. row ***************************
CREATE USER for wildcard@%: CREATE USER 'wildcard'@'%' IDENTIFIED WITH 'mysql_native_password' AS '' REQUIRE NONE PASSWORD EXPIRE DEFAULT ACCOUNT UNLOCK
1 row in set (0.0022 sec)

sql> 
Bye!
[dvaneeden@dve-carbon ~]$ mysqlsh mysql://wildcard@192.168.1.54:4000
Please provide the password for 'wildcard@192.168.1.54:4000': 
Save password for 'wildcard@192.168.1.54:4000'? [Y]es/[N]o/Ne[v]er (default No): 

sql> USE mysql
MySQL Error 1044: Access denied for user 'wildcard'@'%' to database 'mysql'

sql> 
Bye!
[dvaneeden@dve-carbon ~]$ mysqlsh mysql://specifichost@192.168.1.54:4000
Please provide the password for 'specifichost@192.168.1.54:4000': 
Save password for 'specifichost@192.168.1.54:4000'? [Y]es/[N]o/Ne[v]er (default No): 

sql> USE mysql
MySQL Error 1044: Access denied for user 'specifichost'@'192.168.1.54' to database 'mysql'

sql> SELECT tidb_version()\G
*************************** 1. row ***************************
tidb_version(): Release Version: v5.4.0-alpha-274-g13d0deb7f
Edition: Community
Git Commit Hash: 13d0deb7fef7fd7391dce19f320abef4256223bd
Git Branch: master
UTC Build Time: 2021-12-01 08:28:22
GoVersion: go1.16.8
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false
1 row in set (0.0005 sec)

[morgo]

I added this for future checking.

The case where it currently fails prior to this is the Column name in SHOW GRANTS FOR CURRENT_USER(). But in the tests I didn't find an example where we check column names.

[tiancaiamao]

NOTE: This totally change the semantic of the old API, and all the code referencing of the old API might be affected.

AuthIdentityString() -> String()
String() -> LoginString()

I can't say the new API is better or necessay (Go also discourage public API change), but as long as it fix more cases and do not introduce regression, it looks good to me.

[Defined2014]

/run-check_dev_2

[xiongjiwei]

/merge

[ti-chi-bot]

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

Commit hash: 83645fc

[ti-srebot]

cherry pick to release-5.3 in PR #30474