Improve local password collection (#257)

- Resolves an issue where by if we accept a local password over 32 bytes we'll crash at key generation
  time. Instead, we now warn if the password is over 32 chars and prompt the user to try again. On the
  third attempt we throw a provider error.
 - To go along with the above, we now will warn the user if confirmation of a local password
   does not match the original entered local password vs immediately throwing, instead the user has 3 attempts
   to correctly confirm.

src/rebar3_hex_user.erl

@@ -86,6 +86,8 @@ format_error({generate_key, Reason}) ->
     io_lib:format("Failure generating authentication tokens: ~ts", [Reason]);
 format_error(no_match_local_password) ->
     "Password confirmation failed. The passwords must match.";
+format_error(local_password_too_big) ->
+    "Local passwords can not exceed 32 characters.";
 format_error(bad_command) ->
     "Command must be one of register, whoami, auth, deauth or reset_password";
 format_error(Reason) ->
@@ -137,14 +139,37 @@ auth(Repo, State) ->
                 "Hex requires you to have a local password that applies only to this machine for security "
                 "purposes. Please enter it."),
 
-    LocalPassword = rebar3_hex_io:get_password(<<"Local Password: ">>),
-    ConfirmLocalPassword = rebar3_hex_io:get_password(<<"Local Password (confirm): ">>),
 
-    case LocalPassword =:= ConfirmLocalPassword of
-        true ->
-            generate_all_keys(Username, Password, LocalPassword, Repo, State);
-        false ->
-            throw(?PRV_ERROR(no_match_local_password))
+    MaxRetries = 3,
+    LocalPassword = get_local_password(<<"Local Password: ">>, MaxRetries),
+    ok = confirm_local_password(<<"Local Password (confirm): ">>, LocalPassword, MaxRetries),
+    generate_all_keys(Username, Password, LocalPassword, Repo, State).
+
+
+get_local_password(_Prompt, 0) -> 
+    throw(?PRV_ERROR(local_password_too_big));
+
+get_local_password(Prompt, MaxRetries) ->
+    case rebar3_hex_io:get_password(Prompt) of
+        Pw when byte_size(Pw) > 32 ->
+            Warn = "Local passwords can not be greater than 32 characters, please try again",
+            rebar_log:log(warn, Warn, []),
+            get_local_password(Prompt, MaxRetries - 1);
+        Pw -> 
+            Pw
+    end.
+
+confirm_local_password(_Prompt, _ExpectedPw, 0) ->
+   throw(?PRV_ERROR(no_match_local_password)); 
+
+confirm_local_password(Prompt, ExpectedPw, MaxRetries) -> 
+     case rebar3_hex_io:get_password(Prompt) of
+        Pw when Pw =:= ExpectedPw ->
+            ok;
+        _ ->
+          Warn = "Passwords do not match, please try again",
+          rebar_log:log(warn, Warn, []),
+          confirm_local_password(Prompt, ExpectedPw, MaxRetries - 1)
     end.
 
 deauth(#{username := Username, name := RepoName}, State) ->