support git remotes that need http basic auth

using git credential to get the password

One thing this doesn't do is wrap the password prompting inside the prompt
action. So with -J, the output can be a bit garbled.

Git/Credential.hs

@@ -1,6 +1,6 @@
 {- git credential interface
  -
- - Copyright 2019 Joey Hess <id@joeyh.name>
+ - Copyright 2019-2020 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -22,6 +22,23 @@ credentialUsername = M.lookup "username" . fromCredential
 credentialPassword :: Credential -> Maybe String
 credentialPassword = M.lookup "password" . fromCredential
 
+credentialBasicAuth :: Credential -> Maybe BasicAuth
+credentialBasicAuth cred = BasicAuth
+	<$> credentialUsername cred
+	<*> credentialPassword cred
+
+getBasicAuthFromCredential :: Repo -> GetBasicAuth
+getBasicAuthFromCredential r u = do
+	c <- getUrlCredential u r
+	case credentialBasicAuth c of
+		Just ba -> return $ Just (ba, signalsuccess c)
+		Nothing -> do
+			signalsuccess c False
+			return Nothing
+  where
+	signalsuccess c True = approveUrlCredential c r
+	signalsuccess c False = rejectUrlCredential c r
+
 -- | This may prompt the user for login information, or get cached login
 -- information.
 getUrlCredential :: URLString -> Repo -> IO Credential