Functions for OAuth 2.0 authentication for Google APIs.

If you are new to Google web API's, bear in mind that there are three different methods for accessing APIs (installed applications, web apps, service-to-service), and this library is most useful for "installed applications".

Installed applications need the user to grant permission in a browser at least once (see formUrl). However, while the resulting accessToken expires quickly, the refreshToken can be used indefinitely for retrieving new access tokens. Thus this approach can be suitable for long running or periodic programs that access Google data.

Below is a quick-start program which will list any Google Fusion tables the user possesses. It requires the client ID and secret retrieved from https://code.google.com/apis/console.

 import Control.Monad (unless)
 import System.Info (os)
 import System.Process (system, rawSystem)
 import System.Exit    (ExitCode(..))
 import System.Directory (doesFileExist)
 import Network.Google.OAuth2 (formUrl, exchangeCode, refreshTokens,
                               OAuth2Client(..), OAuth2Tokens(..))
 import Network.Google (makeRequest, doRequest)
 import Network.HTTP.Conduit (simpleHttp)
 --
 cid    = "INSTALLED_APP_CLIENT_ID"
 secret = "INSTALLED_APP_SECRET_HERE"
 file   = "./tokens.txt"
 --  
 main = do
   -- Ask for permission to read/write your fusion tables:
   let client = OAuth2Client { clientId = cid, clientSecret = secret }
       permissionUrl = formUrl client ["https:www.googleapis.comauthfusiontables"]
   b <- doesFileExist file
   unless b $ do 
       putStrLn$ "Load this URL: "++show permissionUrl
       case os of
         "linux"  -> rawSystem "gnome-open" [permissionUrl]
         "darwin" -> rawSystem "open"       [permissionUrl]
         _        -> return ExitSuccess
       putStrLn "Please paste the verification code: "
       authcode <- getLine
       tokens   <- exchangeCode client authcode
       putStrLn$ "Received access token: "++show (accessToken tokens)
       tokens2  <- refreshTokens client tokens
       putStrLn$ "As a test, refreshed token: "++show (accessToken tokens2)
       writeFile file (show tokens2)
   accessTok <- fmap (accessToken . read) (readFile file)
   putStrLn "As a test, list the users tables:"
   response <- simpleHttp ("https:www.googleapis.comfusiontablesv1/tables?access_token="++accessTok)
   putStrLn$ BL.unpack response