COM_CHANGE_USER

This command allows a connected client to re-authenticate as a different user without closing and reopening the connection.

COM_CHANGE_USER resets the connection and re-authenticates with the given credentials. The packet is identical to the authentication packet in the connection handshake.

Fields

• int<1> 0x11 : COM_CHANGE_USER header.

• string<NUL> username.

• If (server_capabilities & CLIENT_SECURE_CONNECTION):

  • int<1> length of authentication response.

  • string authentication response.

• Else:

  • string<NUL> authentication response.

• string<NUL> default schema name.

• int<2> client character collation.

• If (server_capabilities & CLIENT_PLUGIN_AUTH):

  • string<NUL> authentication plugin name.

• If (server_capabilities & CLIENT_CONNECT_ATTRS):

  • int<lenenc> size of connection attributes.

  • Loop:

    • string<lenenc> key.

    • string<lenenc> value.

Response

Server response is like connection authentication :

• An OK packet in case of success OK_Packet.

• An error packet in case of error ERR_Packet.

• Authentication switch:

  • If the client or server doesn't have PLUGIN_AUTH capability:

    • Server sends 0xFE byte.

    • Client sends old_password.

  • Else:

    • Server sends Authentication switch request.

    • Client may have many exchanges with the server according to the Plugin.

  • Authentication switch ends with server sending either OK_Packet or ERR_Packet.

If the authentication fails more than three times, all future COM_CHANGE_USER commands on the connection will return the #08S01 Unknown command error. This is an anti-brute-force mechanism designed to prevent rapid guessing of passwords.

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