A Yesod authentication plugin designed to look users up in a Persistent database where the hash of their password is stored.

Release 1.5 is the first of two which remove compatibility with old (pre 1.3) databases. Some other deprecated functionality is removed too. Please see https://github.com/paul-rouse/yesod-auth-hashdb/blob/master/Upgrading.md

To use this in a Yesod application, the foundation data type must be an instance of YesodPersist, and the username and hashed passwords should be added to the database. The following steps give an outline of what is required.

You need a database table to store user records: in a scaffolded site it might look like:

User
    name Text             -- user name used to uniquely identify users
    password Text Maybe   -- password hash for HashDB
    UniqueUser name

Create an instance of HashDBUser for this data type:

import Yesod.Auth.HashDB (HashDBUser(..))
....
instance HashDBUser User where
    userPasswordHash = userPassword
    setPasswordHash h u = u { userPassword = Just h }

In the YesodAuth instance declaration for your app, include authHashDB like so:

import Yesod.Auth.HashDB (authHashDB)
....
instance YesodAuth App where
    ....
    authPlugins _ = [ authHashDB (Just . UniqueUser), .... ]
    getAuthId creds = ... -- Perhaps modify scaffolding: see below

The argument to authHashDB is a function which takes a Text and produces a Maybe containing a Unique value to look up in the User table. The example (Just . UniqueUser) shown here works for the model outlined above.

In the scaffolding, the definition of getAuthId contains code to add a user who is not already in the database. Depending on how users are administered, this may not make sense when using HashDB, so consider whether it should be removed.

For a real application, the developer should provide some sort of of administrative interface for setting passwords; it needs to call setPassword and save the result in the database. However, if you need to initialise the database by hand, you can generate the correct password hash as follows:

ghci -XOverloadedStrings
> import Crypto.PasswordStore
> makePassword "MyPassword" 17

where "17" is the default strength parameter (defaultStrength) used in this module.

Custom Login Form

Instead of using the built-in HTML form, a custom one can be supplied by using authHashDBWithForm instead of authHashDB.

The custom form needs to be given as a function returning a Widget, since it has to build in the supplied "action" URL, and it must provide two text fields called "username" and "password". For example, the following modification of the outline code given above would replace the default form with a very minimal one which has no labels and a simple layout.

instance YesodAuth App where
    ....
    authPlugins _ = [ authHashDBWithForm myform (Just . UniqueUser), .... ]

myform :: Route App -> Widget
myform action = $(whamletFile "templates/loginform.hamlet")

where templates/loginform.hamlet contains

<form method="post" action="@{action}">
    <input name="username">
    <input type="password" name="password">
    <input type="submit" value="Login">

If a CSRF token needs to be embedded in a custom form, code must be included in the widget to add it - see defaultForm in the source code of this module for an example.