Migrating old md5 passwords to bcrypt with Laravel 5.2's built in auth

I'm migrating an old PHP app over to Laravel 5.2. The app has a huge users table (about 50K users) and the passwords are all MD5 hashes.

Obviously this is unacceptable but rather than sending out an email to all 50,000 users asking them to reset their passwords, I want to change the passwords to bcrypt hashes behind the scenes.

To do this, I want to create an old_password column with the MD5 hash in it and then whenever a user logs in, I check the password against the MD5 hash (if it exists) and then make a new bcrypt hash for next time, deleting the MD5 hash.

I've seen a few examples about how to do this (such as this and this), but none specifically for Laravel 5 and none specifically for use with Laravel 5.2's built in auth.

Is there a clean way to adapt the built-in auth to do this, or am I better off writing my own manual auth system in this case?

via Chebli Mohamed