Hooking into drupal's password mechanism

Question

I'm converting a site from a forum system (mybb) into a drupal site and obviously the password schemes are completely different.

I'm planning on importing all of the users with their old password hashes prefixed with "mybb_".

I'd like to write a module which detects prefixed passwords if the user logs in authenticates using the old mechanism and then replaces the password with a drupal 7 hashed password.

I'm relatively new to drupal development so I'm not familiar enough with the hooks, etc needed to do this.

Any guidance would be great :)

(Also if there is a better way of dealing with this than I have proposed, please feel free to chime in.)

Answer 1

Drupal does similar checks in the function user_check_password(). It is called by the validation function user_login_authenticate_validate() so you could override this using hook_form_alter() and point to a custom version of user_check_password() that includes your mybb check.

Another way, instead of overriding, just add a validation handler in the login form before the default ones and detect, authenticate, and rehash the password there.