Authentication Modules in MaxScale

This document describes the modular authentication in MaxScale. It contains protocol specific information on authentication and how it is handled in MaxScale.

The constants described in this document are defined in the authenticator.h header unless otherwise mentioned.

Authenticator initialization

When the authentication module is first loaded, the initialize entry point is called. The return value of this function will be passed as the first argument to the other entry points.

The loadUsers entry point of the client side authenticator is called when a service starts. The authenticator can load external user data when this entry point is called. This entry point is also called when user authentication has failed and the external user data needs to be refreshed.

When a connection is created, the create entry point is called to create per connection data. The return value of this function is stored in the dcb->authenticator_data field of the DCB object. This data is freed in the destroy entry point and the value returned by create will be given as the first parameter.

MySQL Authentication Moduels

The MySQL protocol authentication starts when the server sends the handshake packet to the client to which the client responds with a handshake response packet. If the server is using the default mysql_native_password authentication plugin, the server responds with either an OK packet or an ERR packet and the authentication is complete.

If a different authentication plugin is required to complete the authentication, instead of sending an OK or ERR packet, the server responds with an AuthSwitchRequest packet. This is where the pluggable authentication in MaxScale starts.

Client authentication in MaxScale

The first packet the client side authenticator plugins will receive is the client's handshake response packet.

The client protocol module will call the extract entry point of the authenticator where the authenticator should extract client information. If the extract entry point returns one of the following constants, the authenticate entry point will be called.

  • MXS_AUTH_SUCCEEDED
  • MXS_AUTH_INCOMPLETE
  • MXS_AUTH_SSL_INCOMPLETE

The authenticate entry point is where the authenticator plugin should authenticate the client. If authentication is successful, the authenticate entry point should return MXS_AUTH_SUCCEEDED. If authentication is not yet complete or if the authentication module should be changed, the authenticate entry point should return MXS_AUTH_INCOMPLETE.

Authenticator plugins which do not use the default mysql_native_password authentication plugin should send an AuthSwitchRequest packet to the client and return MXS_AUTH_INCOMPLETE. When more data is available, the extract and authenticate entry points will be called again.

If either of the aforementioned entry points returns one of the following constants, the authentication is considered to have failed and the session will be closed.

  • MXS_AUTH_FAILED
  • MXS_AUTH_FAILED_DB
  • MXS_AUTH_FAILED_SSL

Read the individual authenticator module documentation for more details on the authentication process of each authentication plugin.

Backend authentication in MaxScale

The first packet the authentication plugins in MaxScale will receive is either the AuthSwitchRequest packet or, in case of mysql_native_password, the OK packet. At this point, the protocol plugin will call the extract entry point of the backend authenticator. If the return value of the call is one of the following constants, the protocol plugin will call the authenticate entry point of the authenticator.

  • MXS_AUTH_SUCCEEDED
  • MXS_AUTH_INCOMPLETE
  • MXS_AUTH_SSL_INCOMPLETE

If the authenticate entry point returns MXS_AUTH_SUCCEEDED, then authentication is complete and any queued queries from the clients will be sent to the backend server. If the return value is MXS_AUTH_INCOMPLETE or MXS_AUTH_SSL_INCOMPLETE, the protocol module will continue the authentication by calling the extract entry point once more data is available.

If either of the aforementioned entry points returns one of the following constants, the authentication is considered to have failed and the session will be closed.

  • MXS_AUTH_FAILED
  • MXS_AUTH_FAILED_DB
  • MXS_AUTH_FAILED_SSL

Read the individual authenticator module documentation for more details on the authentication process of each authentication plugin.