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.

• 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).

• Use newEmptyTokenStore to create a new token stores (token stores are basically TVars containing the tokens wrapped in Either SomeException).

• 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.

• To use the current token, extract it from the TVar using readTVar (and pattern matching on Right).

{-# LANGUAGE OverloadedStrings   #-}

data TokenFoo

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

createTokenStoreFoo :: LoggingT IO (TokenStore TokenFoo)
createTokenStoreFoo = 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