Using HashDB In a Scaffolded Site

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Example with Yesod Scaffold and Your Own Model:

1. Your object representing clients must provide a unique identifier field, a field for the password hash, and a field for the password salt. Example:

   -- in config/models
   
   Person
       email    Text
       password Text
       UniqueEmail email
       deriving Typeable

   In this example, 'email' will be the unique identifier.

2. You must provide

   instance HashDBUser (<yourObject>Generic backend)

   in the module that shares your model. In the scaffolded site, that module is Model. Continuing the Person example,

   -- in Model.hs
   import Yesod.Auth.HashDB (HashDBUser(..))
   
   instance HashDBUser Person where
       userPasswordHash = Just . personPassword
       setPasswordHash h p = p { personPassword = h }

3. Now, in Foundation.hs, we hook Auth.HashDB into your foundation. You must add an import of Yesod.Auth.HashDB, of course,

   import Yesod.Auth.HashDB (authHashDB, getAuthIdHashDB)

   and then modify the YesodAuth instance like so:

   -- in Foundation.hs
   instance YesodAuth <MySite> where
       type AuthId <MySite> = PersonId
       -- ... loginDest, etc.
       getAuthId creds = getAuthIdHashDB AuthR (Just . UniqueEmail) creds
       authPlugins _ = [authHashDB (Just . UniqueEmail)]

Further examples can be found in the module documentation