signurl.hs

import           Data.ByteString (ByteString)
import qualified Data.ByteString.Char8 as C (pack, unpack)
import qualified Data.ByteString.Lazy as L (fromChunks)
import qualified Data.ByteString.Lazy.Char8 as LC (pack)
import           Data.Digest.Pure.SHA (hmacSha1, showDigest)
import           Data.List (sort)
import           Network.URL (URL(..), importURL, exportURL, exportParams, add_param)

-- | Calculate the SHA-1 HMAC of the parameters and include it as the parameter "h".
signParameters :: ByteString    -- | The key for HMAC.
               -> URL           -- | The URL to sign.
               -> URL
signParameters key url = 
    let params = LC.pack $ exportParams $ sort $ url_params url
        sig = showDigest $ hmacSha1 (L.fromChunks [key]) params
    in add_param url ("h", sig)


-- | Sign a URL.
--
-- Returned Nothing when importURL is unable to parse the input URL.
signURL :: ByteString   -- ^ The key for HMAC.
        -> ByteString   -- ^ The URL to be signed.
        -> Maybe ByteString
signURL key url = do
    url' <- importURL $ C.unpack url
    let params = LC.pack $ exportParams $ sort $ url_params url'
    let sig = showDigest $ hmacSha1 (L.fromChunks [key]) params
    let url'' = add_param url' ("h", sig)
    return $ C.pack $ exportURL $ url''