Remove default credentials

ANONYMOUS is the default and username/password must be provided as soon
as PLAIN is used.

Author: acogoluegnes

src/main/java/com/rabbitmq/client/amqp/impl/DefaultConnectionSettings.java

@@ -48,17 +48,14 @@ abstract class DefaultConnectionSettings<T> implements ConnectionSettings<T> {
           SASL_MECHANISM_ANONYMOUS,
           SASL_MECHANISM_EXTERNAL);
 
-  static final String DEFAULT_USERNAME = "guest";
-  static final String DEFAULT_PASSWORD = DEFAULT_USERNAME;
   static final String DEFAULT_HOST = "localhost";
   static final int DEFAULT_PORT = 5672;
   static final int DEFAULT_TLS_PORT = 5671;
   static final String DEFAULT_VIRTUAL_HOST = "/";
 
   private String host = DEFAULT_HOST;
   private int port = DEFAULT_PORT;
-  private CredentialsProvider credentialsProvider =
-      new DefaultUsernamePasswordCredentialsProvider(DEFAULT_USERNAME, DEFAULT_PASSWORD);
+  private CredentialsProvider credentialsProvider;
   private String virtualHost = DEFAULT_VIRTUAL_HOST;
   private List<URI> uris = Collections.emptyList();
   private Duration idleTimeout = Duration.ofMillis(ConnectionOptions.DEFAULT_IDLE_TIMEOUT);
@@ -173,14 +170,7 @@ public T saslMechanism(String mechanism) {
               SASL_MECHANISMS.stream().map(n -> "'" + n + "'").collect(Collectors.joining(", "))));
     }
     this.saslMechanism = mechanism;
-    if (SASL_MECHANISM_ANONYMOUS.equals(mechanism)) {
-      this.credentialsProvider = null;
-    } else if (SASL_MECHANISM_PLAIN.equals(mechanism)) {
-      this.credentialsProvider =
-          new DefaultUsernamePasswordCredentialsProvider(DEFAULT_USERNAME, DEFAULT_PASSWORD);
-    } else if (SASL_MECHANISM_EXTERNAL.equals(mechanism)) {
-      this.credentialsProvider = null;
-    }
+    this.credentialsProvider = null;
     return this.toReturn();
   }
 

src/test/java/com/rabbitmq/client/amqp/impl/ConnectionSettingsTest.java

@@ -18,8 +18,6 @@
 package com.rabbitmq.client.amqp.impl;
 
 import static com.rabbitmq.client.amqp.ConnectionSettings.SASL_MECHANISM_PLAIN;
-import static com.rabbitmq.client.amqp.impl.DefaultConnectionSettings.DEFAULT_PASSWORD;
-import static com.rabbitmq.client.amqp.impl.DefaultConnectionSettings.DEFAULT_USERNAME;
 
 import com.rabbitmq.client.amqp.DefaultUsernamePasswordCredentialsProvider;
 import com.rabbitmq.client.amqp.Environment;
@@ -50,6 +48,7 @@ void environmentCredentialsProviderShouldNotBeUsedIfOneSetForConnection() {
     try (Environment environment =
         TestUtils.environmentBuilder()
             .connectionSettings()
+            .saslMechanism(SASL_MECHANISM_PLAIN)
             .credentialsProvider(new LatchCredentialsProvider(environmentUsernameReturnedLatch))
             .environmentBuilder()
             .build()) {
@@ -69,7 +68,7 @@ private static class LatchCredentialsProvider extends DefaultUsernamePasswordCre
     private final CountDownLatch latch;
 
     public LatchCredentialsProvider(CountDownLatch latch) {
-      super(DEFAULT_USERNAME, DEFAULT_PASSWORD);
+      super("guest", "guest");
       this.latch = latch;
     }