[FLINK-5055][security] skip Hadoop UGI login if unsecured

The new Kerberos authentication code in Flink assumed that it's running
against vanilla Hadoop. Original Hadoop's behavior is to skip a secure
login if security is not configured. This is different for other
distributions, e.g. the MapR Hadoop distribution of Hadoop.

Thus, we need to make sure we don't perform any login action if security
is not configured.

This also performs minor code cleanup.

This closes apache#2864.

flink-clients/src/main/java/org/apache/flink/client/CliFrontend.java

@@ -70,7 +70,7 @@
 import org.apache.flink.runtime.messages.JobManagerMessages.StoppingFailure;
 import org.apache.flink.runtime.messages.JobManagerMessages.TriggerSavepoint;
 import org.apache.flink.runtime.messages.JobManagerMessages.TriggerSavepointSuccess;
-import org.apache.flink.runtime.security.SecurityContext;
+import org.apache.flink.runtime.security.SecurityUtils;
 import org.apache.flink.runtime.util.EnvironmentInformation;
 import org.apache.flink.util.Preconditions;
 import org.apache.flink.util.StringUtils;
@@ -97,6 +97,7 @@
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.Callable;
 import java.util.concurrent.TimeUnit;
 
 import static org.apache.flink.runtime.messages.JobManagerMessages.DisposeSavepoint;
@@ -1111,11 +1112,11 @@ public static void main(final String[] args) {
 
 		try {
 			final CliFrontend cli = new CliFrontend();
-			SecurityContext.install(new SecurityContext.SecurityConfiguration().setFlinkConfiguration(cli.config));
-			int retCode = SecurityContext.getInstalled()
-					.runSecured(new SecurityContext.FlinkSecuredRunner<Integer>() {
+			SecurityUtils.install(new SecurityUtils.SecurityConfiguration(cli.config));
+			int retCode = SecurityUtils.getInstalledContext()
+					.runSecured(new Callable<Integer>() {
 						@Override
-						public Integer run() {
+						public Integer call() {
 							return cli.parseParameters(args);
 						}
 					});

flink-runtime/src/main/java/org/apache/flink/runtime/security/HadoopSecurityContext.java

@@ -0,0 +1,49 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.flink.runtime.security;
+
+import org.apache.flink.util.Preconditions;
+import org.apache.hadoop.security.UserGroupInformation;
+
+import java.security.PrivilegedExceptionAction;
+import java.util.concurrent.Callable;
+
+/*
+ * Process-wide security context object which initializes UGI with appropriate security credentials and also it
+ * creates in-memory JAAS configuration object which will serve appropriate ApplicationConfigurationEntry for the
+ * connector login module implementation that authenticates Kerberos identity using SASL/JAAS based mechanism.
+ */
+class HadoopSecurityContext implements SecurityContext {
+
+	private UserGroupInformation ugi;
+
+	HadoopSecurityContext(UserGroupInformation ugi) {
+		this.ugi = Preconditions.checkNotNull(ugi, "UGI passed cannot be null");
+	}
+
+	public <T> T runSecured(final Callable<T> securedCallable) throws Exception {
+		return ugi.doAs(new PrivilegedExceptionAction<T>() {
+			@Override
+			public T run() throws Exception {
+				return securedCallable.call();
+			}
+		});
+	}
+
+}

flink-runtime/src/main/java/org/apache/flink/runtime/security/NoOpSecurityContext.java

@@ -0,0 +1,32 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.apache.flink.runtime.security;
+
+import java.util.concurrent.Callable;
+
+/**
+ * A security context that simply runs a Callable without performing a login action.
+ */
+class NoOpSecurityContext implements SecurityContext {
+
+	@Override
+	public <T> T runSecured(Callable<T> securedCallable) throws Exception {
+		return securedCallable.call();
+	}
+
+}