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diff --git a/src/Reaktor/Plugins/SASL.hs b/src/Reaktor/Plugins/SASL.hs
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+++ b/src/Reaktor/Plugins/SASL.hs
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+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+module Reaktor.Plugins.SASL where
+
+import Data.Aeson
+import Data.Aeson.Types (typeMismatch)
+import Data.Base64.Types (extractBase64)
+import Data.Text qualified as Text
+import Data.Text.Encoding.Base64 (encodeBase64)
+import Prelude.Extended
+import Reaktor
+import Text.Read (readMaybe)
+
+
+data Mechanism = PLAIN
+  deriving (Read, Show)
+
+instance ToJSON Mechanism where
+  toJSON = String . Text.show
+
+instance FromJSON Mechanism where
+  parseJSON = withText "Mechanism" $ \s ->
+    case readMaybe (Text.unpack s) of
+      Just x  -> pure x
+      Nothing -> fail "Invalid Mechanism value"
+
+
+data Config = Config
+    { cMechanism :: Mechanism
+    , cUserName :: Text
+    , cPassword :: Text
+    }
+
+instance Default Config where
+  def = Config
+          { cMechanism = PLAIN
+          , cUserName = ""
+          , cPassword = ""
+          }
+
+instance FromJSON Config where
+  parseJSON = \case
+    Object v ->
+      Config
+        <$> v .:? "mechanism" .!= PLAIN
+        <*> v .: "username"
+        <*> v .: "password"
+    invalid ->
+      typeMismatch "Config" invalid
+
+
+new :: Config -> Actions -> IO (Message -> IO ())
+new Config{..} Actions{..} =
+    return $ \case
+      Start | cUserName /= "" && cPassword /= "" -> do
+        aSend (Message Nothing CAP ["REQ", "sasl"])
+
+      Message _ CAP [_username, "ACK", "sasl"] -> do
+        aSend (Message Nothing AUTHENTICATE [Text.show cMechanism])
+
+      Message _ AUTHENTICATE ["+"] ->
+        case cMechanism of
+          PLAIN ->
+            mapM_ (\chunk -> aSend (Message Nothing AUTHENTICATE [chunk]))
+                  (toAuthChunks (toBase64 ("\0" <> cUserName <> "\0" <> cPassword)))
+
+      Message _ RPL_SASLSUCCESS _ ->
+        aSend (Message Nothing CAP ["END"])
+
+      Message _ ERR_SASLFAIL _ ->
+        aSend (Message Nothing CAP ["END"])
+
+      Message _ ERR_SASLTOOLONG _ ->
+        aSend (Message Nothing CAP ["END"])
+
+      Message _ ERR_SASLALREADY _ ->
+        aSend (Message Nothing CAP ["END"])
+
+      _ -> pure ()
+
+
+toBase64 :: Text -> Text
+toBase64 = extractBase64 . encodeBase64
+
+
+-- Split input Text into chunks compatibe with the AUTHENTICATE command.
+-- This function assumes that each character in the input Text is exactly one
+-- byte long, which is true for any Base64 encoded Text.
+--
+-- See also: https://ircv3.net/specs/extensions/sasl-3.1#the-authenticate-command
+toAuthChunks :: Text -> [Text]
+toAuthChunks s =
+    if not (null chunks) && Text.length (last chunks) == 400 then
+      chunks <> ["+"]
+    else
+      chunks
+  where
+    chunks = toChunksOf 400 s
+
+
+toChunksOf :: Int -> Text -> [Text]
+toChunksOf n s
+    | Text.null s = []
+    | otherwise = let (a,b) = Text.splitAt n s
+                  in a : toChunksOf n b