Added Spotify as a supported OAuth2 backend

Yesod/Auth/OAuth2/Spotify.hs

@@ -0,0 +1,61 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Yesod.Auth.OAuth2.Spotify
+    ( oauth2Spotify
+    , module Yesod.Auth.OAuth2
+    ) where
+
+import Control.Applicative ((<$>), (<*>))
+import Control.Exception.Lifted
+import Control.Monad (mzero)
+import Data.Aeson
+import Data.Text (Text)
+import Data.ByteString (ByteString)
+import Data.Text.Encoding (encodeUtf8)
+import Network.HTTP.Conduit(Manager)
+import Yesod.Auth
+import Yesod.Auth.OAuth2
+
+data SpotifyUser = SpotifyUser
+    { spotifyUserId          :: Text
+    , spotifyUserHref        :: Text
+    , spotifyUserDisplayName :: Text
+    , spotifyProduct         :: Text
+    }
+
+instance FromJSON SpotifyUser where
+    parseJSON (Object v) = SpotifyUser <$>
+                           v .: "id" <*>
+                           v .: "href" <*>
+                           v .: "display_name" <*>
+                           v .: "product"
+    parseJSON _ = mzero
+
+oauth2Spotify :: YesodAuth m
+             => Text -- ^ Client ID
+             -> Text -- ^ Client Secret
+             -> AuthPlugin m
+oauth2Spotify clientId clientSecret = authOAuth2 "spotify"
+    (OAuth2
+        { oauthClientId            = encodeUtf8 clientId
+        , oauthClientSecret        = encodeUtf8 clientSecret
+        , oauthOAuthorizeEndpoint  = "https://accounts.spotify.com/authorize"
+        , oauthAccessTokenEndpoint = "https://accounts.spotify.com/api/token"
+        , oauthCallback            = Nothing
+        })
+    fetchSpotifyProfile
+
+fetchSpotifyProfile :: Manager -> AccessToken -> IO (Creds m)
+fetchSpotifyProfile manager token = do
+    result <- authGetJSON manager token "https://api.spotify.com/v1/me"
+    case result of
+        Right user -> return $ toCreds user
+        Left err -> throwIO $ InvalidProfileResponse "spotify" err
+
+toCreds :: SpotifyUser -> Creds m
+toCreds user = Creds "spotify"
+    (spotifyUserId user)
+    [ ("href"        , spotifyUserHref user)
+    , ("display_name", spotifyUserDisplayName user)
+    , ("product"     , spotifyProduct user)
+    ]

yesod-auth-oauth2.cabal

@@ -48,6 +48,7 @@ library
                      Yesod.Auth.OAuth2.Google
                      Yesod.Auth.OAuth2.Learn
                      Yesod.Auth.OAuth2.Github
+                     Yesod.Auth.OAuth2.Spotify
 
     ghc-options:     -Wall