This is Haskell library built on top of the async-refresh package implementing the logic for refreshing of expiring access tokens.

• Create new token types. Using the DataKinds extension we can do this via data MyAppTokens = TokenFoo | TokenBar.

• Make the tokens be instances of the IsToken type classes by defining the tokenScopes method and (optionally) tokenName (a human readable label for this token).

• Create new token stores (which are basically TVar's containing the tokens wrapped in Either SomeException) using newEmptyTokenStore`.

• Create a new configuration by adjusting defaultTokenConf using the functions tokenConfAddRequest and tokenConfSetFactor. The function tokenConfAddRequest expects values of type RequestToken — these values encapsulate the token stores together with a token-refreshing action.

• Use newTokenRefresher to initiate token refreshing for each registered token refreshing request.

{-# LANGUAGE DataKinds           #-}
{-# LANGUAGE OverloadedStrings   #-}
{-# LANGUAGE PolyKinds           #-}

data MyAppTokens = TokenFoo | TokenBar

instance IsToken 'TokenFoo where
  tokenScopes _ = ["foo.read", "foo.write"]

createTokenStoreFoo :: IO (TokenStore 'TokenFoo)
createTokenStoreFoo = runStderrLoggingT $ do
  tokenFoo <- newEmptyTokenStore (Proxy :: Proxy 'TokenFoo)
  let conf = defaultTokenConf
             & tokenConfAddRequest (RequestToken tokenFoo actionFoo)
  _ <- newTokenRefresher conf
  return tokenFoo

  where actionFoo :: (MonadIO m, IsToken t) => m (RefreshResult (Token t))
        actionFoo =
          return $ RefreshResult (Token "secret-foo-token") Nothing