Create a login in laravel where credentials are not in the same database

I need to create a login to an existing database in laravel. The database is kinda weird modeled, yet I cannot change it. I'm quite new to laravel and I cannot figure out how it's done. The login with the normal make::auth seems intuitive, but I don't know how to change the parameters, or maybe you provide me with a completely different solution. How would you implement this login?

The credentials are spread out on two tables:

Table: Staff
-----
id
username


Table: Credential
-----
id
password (sha1)
id_staff

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