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1 parent 9f66a95 commit 97c4ed6713a9965de9cfe5a1131250623aa12e63 @ozataman ozataman committed Jan 9, 2011
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-Snap-auth provides authentication functionality for Snap. Eventually this will
-probably be moved into the snap package. But we're starting it off in
-a separate package until we get a better sense of how snap code will be
+Snap-auth provides authentication and session management functionality for
+Snap. Eventually this will probably be moved into the snap package. But we're
+starting it off in a separate package until we get a better sense of how snap
+code will be organized.
-The design philosophy is that we let the user choose a persistence/session
-mechanism consistent with their application. Other than that, we try provide
-a turn-key solution, so as much as possible should be done here. Random salt
-generation, hashing, password verification, etc need special care to ensure the
-cryptographic properties necessary for strong security. The user should not
-have to think about these concerns.
+## The Concept
-We provide some higher level functionality that can be used directly inside
-your application's monad. This functionality helps you determine if there is an
-authenticated user, require that one is present and get their credentials when
+User/session management has two basic levels (potentially more if you add
-A Snap.Auth.Handlers module has also been included with default handlers to
-address typical use cases, such as user signup, login and logout.
+ - Making sure an established session between any user - authenticated or
+ otherwise - and the server stays secure.
+ - Authenticating users, which means having proof that a user is who she says
+ she is before we grant her some important priveleges in our application.
-Currently this code requires the 0.3 branch of the Snap framework, which is due
-to be released in the near future.
+This package both of these challenges. It will likely be integrated into Snap
+as the stock solution, possibly in the 0.5 release.
-TODO List
-* Challenge/response authentication (
+## Session Management
+First, let's demonstrate the session management piece.
+### Introduction
+For those familiar with Rails, the functionality is similar to
+ session[:user_id] = 1234
+ session[:last_query] = "johnpollak"
+The difference, however, is that we can't just store arbitrary data -types and
+instead use only ByteStrings.
+We define a type Session as
+ type Session = Map ByteString ByteString
+which gives us all the convenience and power of Haskell's standard Map library.
+It is yet to be seen if this is effective and/or efficient in the long run but
+has worked well so far.
+### Setting Up Your Application With Sessions
+Let's setup the session functionality using the CookieSession backend.
+ -- Define a field to hold the session state in your application state
+ data ApplicationState = ApplicationState
+ { appSessionSt :: CookieSessionState }
+ -- Instantiate your app as a MonadSession
+ instance HasCookieSessionState ApplicationState where
+ getCookieSessionState = appSessionSt
+ -- Add some simple initializer code
+ appInit :: Initializer ApplicationState
+ appInit = do
+ cs <- cookieSessionStateInitializer $ defCookieSessionState
+ { csKeyPath = "config/site-key.txt"
+ , csCookieName = "myapp-session" }
+ return $ ApplicationState cs
+And you are done. While you have to do this manually for now, we will in the
+future have the snap executable auto-generate some of this boiler plate
+for you.
+### Usage Example
+Let's assume we have an odd desire to persist our user's age in our session
+ import qualified Data.Map as M
+ import Snap.Extension.CookieSession
+ ...
+ myHandler = do
+ setInSession "user_age" "32" -- that's all we have to do!
+ render "pages/myPage"
+The "user_age" field will now be available in this user's session until we
+delete it or expire the session.
+We can now retrieve it at any point with:
+ myHandler2 = do
+ uage <- getFromSession "user_age"
+ doSomethingWithUid uage
+ render "pages/myPage2"
+### Backends
+#### CookieSession
+There is currently a single back-end: Snap.Extension.Session.CookieSession. It
+uses Data.Serialize to serialize the Session data type and Michael Snoyman's
+Web.ClientSession to encrypt the cookie. The cookie is encrypted, which means
+it is fully secure and can't be read by the client/end-user.
+Since this method has no need for a DB back-end, it works out of the box and is
+pretty much the simplest session persistence back-end to use. For those
+familiar, this method is the default behavior in Ruby on Rails as well.
+Please see the Haddock documentation for more information.
+### Other Backends
+The idea would be to add various other back-ends as desired. Redis, MongoDB,
+SQL-based databases, etc. should all be straightforward enough to implement. We
+would just need a scheme to presist the session type in the respective
+## Authentication
+The second layer of thic package provides for user athentication. It defines an
+AuthUser datatype that holds all of the core authentication fields for
+a "user". Let's look at it so we can get a sense for what is possible:
+ data AuthUser = AuthUser
+ { userId :: Maybe UserId
+ , userEmail :: Maybe ByteString
+ , userPassword :: Maybe Password
+ , userSalt :: Maybe ByteString
+ , userActivatedAt :: Maybe UTCTime
+ , userSuspendedAt :: Maybe UTCTime
+ , userLoginCount :: Int
+ , userFailedLoginCount :: Int
+ , userCurrentLoginAt :: Maybe UTCTime
+ , userLastLoginAt :: Maybe UTCTime
+ , userCurrentLoginIp :: Maybe ByteString
+ , userLastLoginIp :: Maybe ByteString
+ , userCreatedAt :: Maybe UTCTime
+ , userUpdatedAt :: Maybe UTCTime
+ } deriving (Read,Show,Ord,Eq)
+The authentication piece has two key typeclasses that we need to be aware of.
+### MonadAuth Typeclass
+To enable authentication, we need to make our application monad an instance of
+MonadAuth. While doing so, we get to choose/customize various authentication
+parameters. The simplest way to instantiate our application is simply:
+ instance MonadAuth Application
+and done. That's right, we have all the sensible defaults set up so you could
+potentially just do that. More typically, here is what you would
+ instance MonadAuth Application where
+ authAuthenticationKeys = return ["login", "domain"]
+ authUserTable = return "myusers"
+and so on. Take a look at haddocks to see what can be specified.
+NOTE: We are still working on implementing some of these options, but it should
+be complete soon enough.
+### MonadAuthUser Typeclass
+Now onto the database integration. This typeclass is all about persisting users
+in some form of storage. Whatever snap database extension is being used would
+be expected to instantiate this typeclass and have nice integration with
+As an example, Snap.Extension.DB.MongoDB has ongoing support for MonadAuth and
+instantiates MonadAuthUser for free. See the repo at:
+A couple of key ideas to understand this typeclass are as follows:
+ 1. User can be looked up in 2 ways:
+ - With an internal/db-provided unique bytestring identifier. This is the
+ "id" field in most db systems.
+ - A Map of key, value pairs that can be used to look up a user in the db.
+ This is the external interface and is typically submitted through a web
+ form. This is how the user of you application will identify herself
+ during login.
+ 1. The user table in the DB can contain more fields than necessary for
+ authentication. This is both natural and typical. So the saveAuthUser
+ function takes a (AuthUser, t) input. AuthUser contains the core
+ authentication fields and t is passed directly to the DB back-end to be
+ included in the save. As an example, in MongoDB implementation t is the
+ Document datatype and is merged with the AuthUser fields prior to database
+ save.
+Again, this typeclass is instantiated by the DB extension you are using, so
+normally you should not need to implement it.
+### Usage Example
+Here is a simple example. We'll provide more thorough documentation as things
+ data User = User
+ { authUser :: AuthUser
+ , myField1 :: ByteStrings
+ , myField2 :: ByteStrings
+ }
+ -- Construct your 'User' from the given parameters
+ -- Make sure you do validation as well - at least for now.
+ makeUser ps = return $ User { .... }
+ additionalUserFields :: User -> Document
+ additionalUserFields u = [ "myField1" =: myField1 u
+ , "myField2" =: myField2 u ]
+ site = routes $
+ [ ("/signup", method GET $ newSignupH)
+ , ("/signup", method POST $ signupH)
+ , ("/login", method GET $ newSessionH)
+ , ("/login", method POST $ loginHandler "password" newSessionH redirHome)
+ ]
+ redirHome = redirect "/"
+ -- Make sure you have a 'password' field in there
+ newSessionH = render "login"
+ -- Assuming you have a signup.tpl template
+ newSignupH = render "signup"
+ -- Save user and redirect as appropriate
+ signupH :: Application ()
+ signupH = do
+ ps <- getParams
+ let u = makeUser ps
+ au <- saveAuthUser (u, additionalUserFields u)
+ case au of
+ Nothing -> newSignupH
+ Just au' -> do setSessionUserId $ userId au'
+ redirect "/"
+### Session-related
+#### General
+- Splices/handlers for easy CSRF protection token integration:
+ - csrf_meta_tag for unobtrusive JS based binding to forms (like in Rails 3)
+ - csrf_token_tag for a hidden field inside forms (in progress)
+ - verify_authenticity handler to be chained before your destructive handlers
+#### Planned Back-ends
+- MongoDB backend
+- HDBC-based SQL back-ends once extension-hdbc is in place
+#### Open Questions/Considerations
+- Possibility of using JSON-like datatype for session store.
+### Auth-related
+- Challenge/response authentication (
This is needed to provide secure authentication without SSL. The goal is to
take as much of the burden as possible off the end user, which probably
means including some Javascript code for use on the client side. If the
client is not javascript-enabled, then the user should have the option to
failover seamlessly to less secure authentication (that transmits cleartext
passwords across the network) or alert the user and disallow logins..
-* Support for "remember me" and "password reset" tokens.
+- Support for "remember me" and "password reset" tokens.

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