Add snapshot taker for special StandardUsernamePasswordCredentials impls

src/main/java/com/cloudbees/plugins/credentials/impl/UsernamePasswordCredentialsSnapshotTaker.java

@@ -0,0 +1,30 @@
+package com.cloudbees.plugins.credentials.impl;
+
+import com.cloudbees.plugins.credentials.CredentialsSnapshotTaker;
+import com.cloudbees.plugins.credentials.common.StandardUsernamePasswordCredentials;
+
+import hudson.Extension;
+import hudson.util.Secret;
+
+@Extension
+public class UsernamePasswordCredentialsSnapshotTaker extends CredentialsSnapshotTaker<StandardUsernamePasswordCredentials> {
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public Class<StandardUsernamePasswordCredentials> type() {
+        return StandardUsernamePasswordCredentials.class;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public StandardUsernamePasswordCredentials snapshot(StandardUsernamePasswordCredentials credentials) {
+        if (credentials instanceof UsernamePasswordCredentialsImpl) {
+            return credentials;
+        }
+        return new UsernamePasswordCredentialsImpl(credentials.getScope(), credentials.getId(), credentials.getDescription(), credentials.getUsername(), Secret.toString(credentials.getPassword()));
+    }
+}