# [Known Issues] TiDB returns 'Unknown auth plugin' when some old clients didn't set auth plugin in login request

## Key Words

Unknown auth plugin

## Description

When try to use a MySQL 5.1 Client to connect TiDB v5.2.0, the TiDB returns "1105 Unknown auth plugin" error, but the TiDB v5.1 will not report such errors.

## Root Cause

This is because some old MySQL Clients won't set auth plugin in the login request. In this case, TiDB will return the "1105 Unknown auth plugin" error but MySQL won't.

This is introduced in [https://github.com/pingcap/tidb/pull/24991](https://github.com/pingcap/tidb/pull/24991) 

## Diagnostic Steps

1. MySQL Client reported "Unknown auth plugin" error
2. Use the "mysql --version" command shows the client version is 5.1 or lower
3. The TiDB version is v5.2
4. Use the higher version of MySQL Client can connect TiDB successfully

## Resolution

Upgrade to the v5.2.2 and newer version.

## Workaround

Use the higher version of MySQL Client like 5.7
If you are using Python, please upgrade the Python MySQLdb to the version 1.2.5

## Affected Versions

v5.2.0 - v5.2.1