Add SASL EXTERNAL mechanism

Signed-off-by: Daniele Ricci <daniele.athome@gmail.com>

smack-sasl-provided/src/main/java/org/jivesoftware/smack/sasl/provided/SASLExternalMechanism.java

@@ -0,0 +1,64 @@
+/**
+ *
+ * Copyright © 2014 Daniele Ricci
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smack.sasl.provided;
+
+import javax.security.auth.callback.CallbackHandler;
+
+import org.jivesoftware.smack.SmackException;
+import org.jivesoftware.smack.sasl.SASLMechanism;
+
+import org.jxmpp.util.XmppStringUtils;
+
+/**
+ * Implementation of the SASL-EXTERNAL authentication mechanism
+ * 
+ * @author Daniele Ricci
+ */
+public class SASLExternalMechanism extends SASLMechanism {
+
+    public static final String NAME = EXTERNAL;
+
+    @Override
+    protected void authenticateInternal(CallbackHandler cbh) throws SmackException {
+        throw new UnsupportedOperationException("CallbackHandler not (yet) supported");
+    }
+
+    @Override
+    protected byte[] getAuthenticationText() throws SmackException {
+        if (authenticationId == null) {
+            return null;
+        }
+
+        return toBytes(XmppStringUtils.completeJidFrom(authenticationId, serviceName));
+    }
+
+    @Override
+    public String getName() {
+        return NAME;
+    }
+
+    @Override
+    public int getPriority() {
+        return 510;
+    }
+
+    @Override
+    protected SASLMechanism newInstance() {
+        return new SASLExternalMechanism();
+    }
+
+}

smack-sasl-provided/src/main/java/org/jivesoftware/smack/sasl/provided/SASLProvidedSmackInitializer.java

@@ -26,6 +26,7 @@ public class SASLProvidedSmackInitializer extends SmackAndOsgiInitializer {
 	@Override
 	public List<Exception> initialize() {
 		SASLAuthentication.registerSASLMechanism(new SASLDigestMD5Mechanism());
+		SASLAuthentication.registerSASLMechanism(new SASLExternalMechanism());
 		return null;
 	}