obviate need for data families

servant-client/src/Servant/Client.hs

@@ -415,13 +415,12 @@ instance HasClient api => HasClient (BasicAuth tag realm usr :> api) where
     clientWithRoute (Proxy :: Proxy api) (basicAuthReq val req) baseurl manager
 
 instance ( HasClient api
-         , AuthenticateClientRequest (AuthProtect tag)
          ) => HasClient (AuthProtect tag :> api) where
   type Client (AuthProtect tag :> api)
-    = ClientAuthType (AuthProtect tag) -> Client api
+    = AuthenticateReq (AuthProtect tag) -> Client api
 
-  clientWithRoute Proxy req baseurl manager val =
-    clientWithRoute (Proxy :: Proxy api) (authReq val req) baseurl manager
+  clientWithRoute Proxy req baseurl manager (AuthenticateReq (val,func)) =
+    clientWithRoute (Proxy :: Proxy api) (func val req) baseurl manager
 
 
 {- Note [Non-Empty Content Types]

servant-client/src/Servant/Common/Auth.hs

@@ -1,6 +1,3 @@
-{-# LANGUAGE DataKinds #-}
-{-# LANGUAGE FlexibleInstances #-}
-
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TypeSynonymInstances #-}
 {-# LANGUAGE TypeFamilies      #-}
@@ -8,9 +5,11 @@
 -- | Authentication for clients
 
 module Servant.Common.Auth (
-    AuthenticateClientRequest ( ClientAuthType, authReq )
+    AuthenticateReq(AuthenticateReq, unAuthReq)
+  , AuthClientData
   , BasicAuthData (BasicAuthData, username, password)
   , basicAuthReq
+  , mkAuthenticateReq
   ) where
 
 import Data.ByteString (ByteString)
@@ -31,8 +30,20 @@ basicAuthReq (BasicAuthData user pass) req =
     let authText = decodeUtf8 ("Basic " <> encode (user <> ":" <> pass))
     in addHeader "Authorization" authText req
 
--- | Class to represent the ability to authenticate a 'Request'
--- object. For example, we may add special headers to the 'Request'.
-class AuthenticateClientRequest a where
-  data ClientAuthType a :: *
-  authReq :: ClientAuthType a -> Req -> Req
+-- | For a resource protected by authentication (e.g. AuthProtect), we need
+-- to provide the client with some data used to add authentication data
+-- to a request
+type family AuthClientData a :: *
+
+-- | For better type inference and to avoid usage of a data family, we newtype
+-- wrap the combination of some 'AuthClientData' and a function to add authentication
+-- data to a request
+newtype AuthenticateReq a =
+  AuthenticateReq { unAuthReq :: (AuthClientData a, AuthClientData a -> Req -> Req) }
+
+-- | Handy helper to avoid wrapping datatypes in tuples everywhere.
+mkAuthenticateReq :: AuthClientData a
+                  -> (AuthClientData a -> Req -> Req)
+                  -> AuthenticateReq a
+mkAuthenticateReq val func = AuthenticateReq (val, func)
+