feat: set JDBC credentials from environmental variables

Using the CONNECT_JDBC_CONNECTION_USER and CONNECT_JDBC_CONNECTION_PASSWORD env vars.

Author: pvannierop

src/main/java/io/confluent/connect/jdbc/util/EnvVarsJdbcCredentialsProvider.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2018 Confluent Inc.
+ *
+ * Licensed under the Confluent Community License (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.confluent.io/confluent-community-license
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OF ANY KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations under the License.
+ */
+
+package io.confluent.connect.jdbc.util;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class EnvVarsJdbcCredentialsProvider implements JdbcCredentialsProvider {
+
+  private static final Logger log = LoggerFactory.getLogger(Version.class);
+
+  private static final String ENV_VAR_DB_USERNAME = "CONNECT_JDBC_CONNECTION_USER";
+  private static final String ENV_VAR_DB_PASSWORD = "CONNECT_JDBC_CONNECTION_PASSWORD";
+
+  @Override
+  public JdbcCredentials getJdbcCredentials() {
+    String username = System.getenv(ENV_VAR_DB_USERNAME);
+    String password = System.getenv(ENV_VAR_DB_PASSWORD);
+    if (username == null || password == null) {
+      throw new RuntimeException("Environment variables " + ENV_VAR_DB_USERNAME + " and "
+          + ENV_VAR_DB_PASSWORD + " must be set when using EnvVarsJdbcCredentialsProvider");
+    }
+    log.info("Using JDBC credentials from environment variables " + ENV_VAR_DB_USERNAME + " and "
+        + ENV_VAR_DB_PASSWORD);
+    return new BasicJdbcCredentials(username, password);
+  }
+
+}