diff --git a/yesod-auth-oauth/Yesod/Auth/OAuth.hs b/yesod-auth-oauth/Yesod/Auth/OAuth.hs
index 382cde94..9b1c5e8e 100644
--- a/yesod-auth-oauth/Yesod/Auth/OAuth.hs
+++ b/yesod-auth-oauth/Yesod/Auth/OAuth.hs
@@ -1,39 +1,46 @@
-{-# LANGUAGE QuasiQuotes, OverloadedStrings #-}
-{-# OPTIONS_GHC -fwarn-unused-imports #-}
+{-# LANGUAGE DeriveDataTypeable, OverloadedStrings, QuasiQuotes #-}
 module Yesod.Auth.OAuth
     ( authOAuth
     , oauthUrl
     , authTwitter
     , twitterUrl
-	, authTumblr
-	, tumblrUrl
+	  , authTumblr
+	  , tumblrUrl
     , module Web.Authenticate.OAuth
     ) where
+import           Control.Applicative      ((<$>), (<*>))
+import           Control.Arrow            ((***))
+import           Control.Exception.Lifted
+import           Control.Monad.IO.Class
+import           Data.ByteString          (ByteString)
+import           Data.Maybe
+import           Data.Text                (Text)
+import qualified Data.Text                as T
+import           Data.Text.Encoding       (decodeUtf8With, encodeUtf8)
+import           Data.Text.Encoding.Error (lenientDecode)
+import           Data.Typeable
+import           Web.Authenticate.OAuth
+import           Yesod.Auth
+import           Yesod.Form
+import           Yesod.Handler
+import           Yesod.Widget
 
-import Yesod.Auth
-import Yesod.Form
-import Yesod.Handler
-import Yesod.Widget
-import Web.Authenticate.OAuth
-import Data.Maybe
-import Control.Arrow ((***))
-import Control.Monad.IO.Class
-import Data.Text (Text)
-import qualified Data.Text as T
-import Data.Text.Encoding (encodeUtf8, decodeUtf8With)
-import Data.Text.Encoding.Error (lenientDecode)
-import Data.ByteString (ByteString)
-import Control.Applicative ((<$>), (<*>))
+data YesodOAuthException = CredentialError String Credential
+                         | SessionError String
+                           deriving (Show, Typeable)
+
+instance Exception YesodOAuthException
 
 oauthUrl :: Text -> AuthRoute
 oauthUrl name = PluginR name ["forward"]
 
 authOAuth :: YesodAuth m
           => OAuth                        -- ^ 'OAuth' data-type for signing.
-          -> (Credential -> IO (Creds m)) -- ^ How to extract ident. 
+          -> (Credential -> IO (Creds m)) -- ^ How to extract ident.
           -> AuthPlugin m
 authOAuth oauth mkCreds = AuthPlugin name dispatch login
   where
+    getOAuthSession = maybe (throwIO $ SessionError "") return =<< lookupSession oauthSessionName
     name = T.pack $ oauthServerName oauth
     url = PluginR name []
     lookupTokenSecret = bsToText . fromMaybe "" . lookup "oauth_token_secret" . unCredential
@@ -51,7 +58,7 @@ authOAuth oauth mkCreds = AuthPlugin name dispatch login
         if oauthVersion oauth == OAuth10
           then do
             oaTok  <- runInputGet $ ireq textField "oauth_token"
-            tokSec <- fromJust <$> lookupSession oauthSessionName
+            tokSec <- getOAuthSession
             deleteSession oauthSessionName
             return $ Credential [ ("oauth_token", encodeUtf8 oaTok)
                                 , ("oauth_token_secret", encodeUtf8 tokSec)
@@ -60,7 +67,7 @@ authOAuth oauth mkCreds = AuthPlugin name dispatch login
             (verifier, oaTok) <-
                 runInputGet $ (,) <$> ireq textField "oauth_verifier"
                                   <*> ireq textField "oauth_token"
-            tokSec <- fromJust <$> lookupSession oauthSessionName
+            tokSec <- getOAuthSession
             deleteSession oauthSessionName
             return $ Credential [ ("oauth_verifier", encodeUtf8 verifier)
                                 , ("oauth_token", encodeUtf8 oaTok)
@@ -74,8 +81,13 @@ authOAuth oauth mkCreds = AuthPlugin name dispatch login
     login tm = do
         render <- lift getUrlRender
         let oaUrl = render $ tm $ oauthUrl name
-        addWidget
-          [whamlet| <a href=#{oaUrl}>Login via #{name} |]
+        [whamlet| <a href=#{oaUrl}>Login via #{name} |]
+
+mkExtractCreds name idName (Credential dic) = do
+  let mcrId = decodeUtf8With lenientDecode <$> lookup (encodeUtf8 $ T.pack idName) dic
+  case mcrId of
+    Just crId -> return $ Creds name crId $ map (bsToText *** bsToText) dic
+    Nothing -> throwIO $ CredentialError ("key not found: " ++ idName) (Credential dic)
 
 authTwitter :: YesodAuth m
             => ByteString -- ^ Consumer Key
@@ -83,19 +95,15 @@ authTwitter :: YesodAuth m
             -> AuthPlugin m
 authTwitter key secret = authOAuth
                 (newOAuth { oauthServerName      = "twitter"
-                          , oauthRequestUri      = "https://api.twitter.com/oauth/request_token"
-                          , oauthAccessTokenUri  = "https://api.twitter.com/oauth/access_token"
-                          , oauthAuthorizeUri    =  "https://api.twitter.com/oauth/authorize"
+                          , oauthRequestUri      = "http://twitter.com/oauth/request_token"
+                          , oauthAccessTokenUri  = "http://api.twitter.com/oauth/access_token"
+                          , oauthAuthorizeUri    = "http://api.twitter.com/oauth/authorize"
                           , oauthSignatureMethod = HMACSHA1
                           , oauthConsumerKey     = key
                           , oauthConsumerSecret  = secret
                           , oauthVersion         = OAuth10a
                           })
-                extractCreds
-  where
-    extractCreds (Credential dic) = do
-        let crId = decodeUtf8With lenientDecode $ fromJust $ lookup "screen_name" dic
-        return $ Creds "twitter" crId $ map (bsToText *** bsToText ) dic
+                (mkExtractCreds "twitter" "screen_name")
 
 twitterUrl :: AuthRoute
 twitterUrl = oauthUrl "twitter"
@@ -114,11 +122,7 @@ authTumblr key secret = authOAuth
                           , oauthConsumerSecret  = secret
                           , oauthVersion         = OAuth10a
                           })
-                extractCreds
-  where
-    extractCreds (Credential dic) = do
-        let crId = decodeUtf8With lenientDecode $ fromJust $ lookup "name" dic
-        return $ Creds "tumblr" crId $ map (bsToText *** bsToText ) dic
+                (mkExtractCreds "tumblr" "name")
 
 tumblrUrl :: AuthRoute
 tumblrUrl = oauthUrl "tumblr"