From b2evolution manual

For a list of available hooks, please refer to the Plugin class methods: in general, all methods that are named in "CamelCase" (e.g. DisplayCommentFormFieldset, but not debug_log) are hooking methods, that get called in b2evolution in special places.

[edit] Authentication

To integrate b2evo with another tool, you can use a plugin to authenticate a user based on the other tool's database.

[edit] LoginAttempt

There's a LoginAttempt event, which gets called, if a user is trying to login. By hooking that event, you would first check, if the user already exists in b2evo and if not, authenticate him against another DB and if that matches, create him locally (in b2evo).

The (new or existing) user gets then automatically logged in.

See the LDAP plugin, which uses this event "extensively".