Hide password in exception messages of SocksAuthRequest

Related: netty#3504

Motivation:

There are two places in the SocksAuthRequest constructor where an
IllegalArgumentException is thrown with a password as part of the
exception message.

This constitutes mishandling of confidential information, which can
compromise user privacy and is flagged as critical by security scanners.

Modifications:

Mask the password in the exception messages

Result:

No unexpected password leak

codec-socks/src/main/java/io/netty/handler/codec/socks/SocksAuthRequest.java

@@ -41,14 +41,14 @@ public SocksAuthRequest(String username, String password) {
             throw new NullPointerException("username");
         }
         if (!asciiEncoder.canEncode(username) || !asciiEncoder.canEncode(password)) {
-            throw new IllegalArgumentException(" username: " + username + " or password: " + password +
-                    " values should be in pure ascii");
+            throw new IllegalArgumentException(
+                    "username: " + username + " or password: **** values should be in pure ascii");
         }
         if (username.length() > 255) {
-            throw new IllegalArgumentException(username + " exceeds 255 char limit");
+            throw new IllegalArgumentException("username: " + username + " exceeds 255 char limit");
         }
         if (password.length() > 255) {
-            throw new IllegalArgumentException(password + " exceeds 255 char limit");
+            throw new IllegalArgumentException("password: **** exceeds 255 char limit");
         }
         this.username = username;
         this.password = password;