These packages provides safe and easy-to-use authentication options for
servant. The same API can be protected via:
- basicauth
- cookies
- JWT tokens
| Package | Hackage |
|---|---|
| servant-auth |  |
| servant-auth-server |  |
| servant-auth-client |  |
| servant-auth-swagger |  |
| servant-auth-docs |  |
First some imports:
{-# OPTIONS_GHC -fno-warn-unused-binds #-}
{-# OPTIONS_GHC -fno-warn-deprecations #-}
import Control.Concurrent (forkIO)
import Control.Monad (forever)
import Control.Monad.Trans (liftIO)
import Data.Aeson (FromJSON, ToJSON)
import GHC.Generics (Generic)
import Network.Wai.Handler.Warp (run)
import System.Environment (getArgs)
import Servant
import Servant.Auth.Server
import Servant.Auth.Server.SetCookieOrphan ()servant-auth library introduces a combinator Auth:
data Auth (auths :: [*]) valWhat Auth [Auth1, Auth2] Something :> API means is that API is protected by
either Auth1 or Auth2, and the result of authentication will be of type
AuthResult Something, where :
data AuthResult val
= BadPassword
| NoSuchUser
| Authenticated val
| IndefiniteYour handlers will get a value of type AuthResult Something, and can decide
what to do with it.
data User = User { name :: String, email :: String }
deriving (Eq, Show, Read, Generic)
instance ToJSON User
instance ToJWT User
instance FromJSON User
instance FromJWT User
data Login = Login { username :: String, password :: String }
deriving (Eq, Show, Read, Generic)
instance ToJSON Login
instance FromJSON Login
type Protected
= "name" :> Get '[JSON] String
:<|> "email" :> Get '[JSON] String
-- | 'Protected' will be protected by 'auths', which we still have to specify.
protected :: Servant.Auth.Server.AuthResult User -> Server Protected
-- If we get an "Authenticated v", we can trust the information in v, since
-- it was signed by a key we trust.
protected (Servant.Auth.Server.Authenticated user) = return (name user) :<|> return (email user)
-- Otherwise, we return a 401.
protected _ = throwAll err401
type Unprotected =
"login"
:> ReqBody '[JSON] Login
:> Verb 'POST 204 '[JSON] (Headers '[ Header "Set-Cookie" SetCookie
, Header "Set-Cookie" SetCookie]
NoContent)
:<|> Raw
unprotected :: CookieSettings -> JWTSettings -> Server Unprotected
unprotected cs jwts = checkCreds cs jwts :<|> serveDirectory "example/static"
type API auths = (Servant.Auth.Server.Auth auths User :> Protected) :<|> Unprotected
server :: CookieSettings -> JWTSettings -> Server (API auths)
server cs jwts = protected :<|> unprotected cs jwts
The code is common to all authentications. In order to pick one or more specific authentication methods, all we need to do is provide the expect configuration parameters.
The following example illustrates how to protect an API with tokens.
-- In main, we fork the server, and allow new tokens to be created in the
-- command line for the specified user name and email.
mainWithJWT :: IO ()
mainWithJWT = do
-- We generate the key for signing tokens. This would generally be persisted,
-- and kept safely
myKey <- generateKey
-- Adding some configurations. All authentications require CookieSettings to
-- be in the context.
let jwtCfg = defaultJWTSettings myKey
cfg = defaultCookieSettings :. jwtCfg :. EmptyContext
--- Here we actually make concrete
api = Proxy :: Proxy (API '[JWT])
_ <- forkIO $ run 7249 $ serveWithContext api cfg (server defaultCookieSettings jwtCfg)
putStrLn "Started server on localhost:7249"
putStrLn "Enter name and email separated by a space for a new token"
forever $ do
xs <- words <$> getLine
case xs of
[name', email'] -> do
etoken <- makeJWT (User name' email') jwtCfg Nothing
case etoken of
Left e -> putStrLn $ "Error generating token:t" ++ show e
Right v -> putStrLn $ "New token:\t" ++ show v
_ -> putStrLn "Expecting a name and email separated by spaces"
And indeed:
./readme JWT
Started server on localhost:7249
Enter name and email separated by a space for a new token
alice alice@gmail.com
New token: "eyJhbGciOiJIUzI1NiJ9.eyJkYXQiOnsiZW1haWwiOiJhbGljZUBnbWFpbC5jb20iLCJuYW1lIjoiYWxpY2UifX0.xzOIrx_A9VOKzVO-R1c1JYKBqK9risF625HOxpBzpzE"
curl localhost:7249/name -v
* Hostname was NOT found in DNS cache
* Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 7249 (#0)
> GET /name HTTP/1.1
> User-Agent: curl/7.35.0
> Host: localhost:7249
> Accept: */*
>
< HTTP/1.1 401 Unauthorized
< Transfer-Encoding: chunked
< Date: Wed, 07 Sep 2016 20:17:17 GMT
* Server Warp/3.2.7 is not blacklisted
< Server: Warp/3.2.7
<
* Connection #0 to host localhost left intact
curl -H "Authorization: Bearer eyJhbGciOiJIUzI1NiJ9.eyJkYXQiOnsiZW1haWwiOiJhbGljZUBnbWFpbC5jb20iLCJuYW1lIjoiYWxpY2UifX0.xzOIrx_A9VOKzVO-R1c1JYKBqK9risF625HOxpBzpzE" \
localhost:7249/name -v
* Hostname was NOT found in DNS cache
* Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 7249 (#0)
> GET /name HTTP/1.1
> User-Agent: curl/7.35.0
> Host: localhost:7249
> Accept: */*
> Authorization: Bearer eyJhbGciOiJIUzI1NiJ9.eyJkYXQiOnsiZW1haWwiOiJhbGljZUBnbWFpbC5jb20iLCJuYW1lIjoiYWxpY2UifX0.xzOIrx_A9VOKzVO-R1c1JYKBqK9risF625HOxpBzpzE
>
< HTTP/1.1 200 OK
< Transfer-Encoding: chunked
< Date: Wed, 07 Sep 2016 20:16:11 GMT
* Server Warp/3.2.7 is not blacklisted
< Server: Warp/3.2.7
< Content-Type: application/json
< Set-Cookie: JWT-Cookie=eyJhbGciOiJIUzI1NiJ9.eyJkYXQiOnsiZW1haWwiOiJhbGljZUBnbWFpbC5jb20iLCJuYW1lIjoiYWxpY2UifX0.xzOIrx_A9VOKzVO-R1c1JYKBqK9risF625HOxpBzpzE; HttpOnly; Secure
< Set-Cookie: XSRF-TOKEN=TWcdPnHr2QHcVyTw/TTBLQ==; Secure
<
* Connection #0 to host localhost left intact
"alice"%
What if, in addition to API tokens, we want to expose our API to browsers? All we need to do is say so!
mainWithCookies :: IO ()
mainWithCookies = do
-- We *also* need a key to sign the cookies
myKey <- generateKey
-- Adding some configurations. 'Cookie' requires, in addition to
-- CookieSettings, JWTSettings (for signing), so everything is just as before
let jwtCfg = defaultJWTSettings myKey
cfg = defaultCookieSettings :. jwtCfg :. EmptyContext
--- Here is the actual change
api = Proxy :: Proxy (API '[Cookie])
run 7249 $ serveWithContext api cfg (server defaultCookieSettings jwtCfg)
-- Here is the login handler
checkCreds :: CookieSettings
-> JWTSettings
-> Login
-> Handler (Headers '[ Header "Set-Cookie" SetCookie
, Header "Set-Cookie" SetCookie]
NoContent)
checkCreds cookieSettings jwtSettings (Login "Ali Baba" "Open Sesame") = do
-- Usually you would ask a database for the user info. This is just a
-- regular servant handler, so you can follow your normal database access
-- patterns (including using 'enter').
let usr = User "Ali Baba" "ali@email.com"
mApplyCookies <- liftIO $ acceptLogin cookieSettings jwtSettings usr
case mApplyCookies of
Nothing -> throwError err401
Just applyCookies -> return $ applyCookies NoContent
checkCreds _ _ _ = throwError err401XSRF protection works by requiring that there be a header of the same value as
a distinguished cookie that is set by the server on each request. What the
cookie and header name are can be configured (see xsrfCookieName and
xsrfHeaderName in CookieSettings), but by default they are "XSRF-TOKEN" and
"X-XSRF-TOKEN". This means that, if your client is a browser and you're using
cookies, Javascript on the client must set the header of each request by
reading the cookie. For jQuery, and with the default values, that might be:
var token = (function() {
r = document.cookie.match(new RegExp('XSRF-TOKEN=([^;]+)'))
if (r) return r[1];
)();
$.ajaxPrefilter(function(opts, origOpts, xhr) {
xhr.setRequestHeader('X-XSRF-TOKEN', token);
}I believe nothing at all needs to be done if you're using Angular's $http
directive, but I haven't tested this.
XSRF protection can be disabled just for GET requests by setting
xsrfExcludeGet = False. You might want this if you're relying on the browser
to navigate between pages that require cookie authentication.
XSRF protection can be completely disabled by setting cookieXsrfSetting = Nothing in CookieSettings. This is not recommended! If your cookie
authenticated web application runs any javascript, it's recommended to send the
XSRF header. However, if your web application runs no javascript, disabling
XSRF entirely may be required.
This README is a literate haskell file. Here is 'main', allowing you to pick between the examples above.
main :: IO ()
main = do
args <- getArgs
let usage = "Usage: readme (JWT|Cookie)"
case args of
["JWT"] -> mainWithJWT
["Cookie"] -> mainWithCookies
e -> putStrLn $ "Arguments: \"" ++ unwords e ++ "\" not understood\n" ++ usage