Add sample java app to access sql using krb auth

sample/java-sample-app/README.md

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+# SQL Server Kerberos Authentication Java Application
+
+A simple Java application that connects to Microsoft SQL Server using Kerberos authentication and executes a simple Select command on the database.
+
+## Prerequisites
+
+- Java 11 or higher
+- Microsoft JDBC Driver for SQL Server (JDBC driver used to create this app is ```mssql-jdbc-12.8.1.jre8.jar```)
+- Valid Kerberos ticket (can be verified using `klist`)
+- SQL Server configured for Kerberos authentication
+
+## Files Required
+
+1. `SQLServerKerberosConnection.class` - The compiled Java class file
+2. `mssql-jdbc-12.8.1.jre8.jar` - Microsoft JDBC driver for SQL Server
+
+## Environment Setup
+
+1. Ensure you have a valid Kerberos ticket:
+```
+klist
+```
+
+2. set the ```KRB5CCNAME``` in the environment to the krb5cc directory of a ticket. For example:
+```
+export KRB5CCNAME=/var/credentials-fetcher/krbdir/<lease_id>/WebApp01/krb5cc
+```
+Verify that the variable has been set correctly using ```echo $KRB5CCNAME```
+
+3. Compile and run the Java file like so
+```
+javac --release 11 -cp .:mssql-jdbc-12.8.1.jre8.jar SQLServerKerberosConnection.java
+java -cp .:mssql-jdbc-12.8.1.jre8.jar SQLServerKerberosConnection
+```
+
+4. You should see the following output
+```
+Connected successfully using Kerberos authentication.
++---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+
+| EmpID                     | EmpName                   | Designation               | Department                | JoiningDate               |
++---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+
+| 1                         | CHIN YEN                  | LAB ASSISTANT             | LAB                       | 2022-03-05 03:57:09.967   |
++---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+
+| 2                         | MIKE PEARL                | SENIOR ACCOUNTANT         | ACCOUNTS                  | 2022-03-05 03:57:09.967   |
++---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+
+| 3                         | GREEN FIELD               | ACCOUNTANT                | ACCOUNTS                  | 2022-03-05 03:57:09.967   |
++---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+
+| 4                         | DEWANE PAUL               | PROGRAMMER                | IT                        | 2022-03-05 03:57:09.967   |
++---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+
+| 5                         | MATTS                     | SR. PROGRAMMER            | IT                        | 2022-03-05 03:57:09.967   |
++---------------------------+---------------------------+---------------------------+---------------------------+---------------------------+
+| 6                         | PLANK OTO                 | ACCOUNTANT                | ACCOUNTS                  | 2022-03-05 03:57:09.967   |
+```

sample/java-sample-app/SQLServerKerberosConnection.java

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+import java.sql.*;
+
+// Replace user, domain name, and server name before compiling
+
+public class SQLServerKerberosConnection {
+    public static void main(String[] args) {
+
+        System.setProperty("java.security.krb5.principal", "<user>@<domain_name>");
+
+        String connectionUrl = "jdbc:sqlserver://<server_name>:1433;"
+                + "databaseName=EmployeesDB;"
+                + "integratedSecurity=true;"
+                + "authenticationScheme=JavaKerberos;"
+                + "userName=<user>@<DOMAIN_NAME>;"
+                + "serverSpn=MSSQLSvc/<server_name>:1433;"
+                + "trustServerCertificate=true";
+
+        try {
+            // Ensure the JDBC driver is loaded
+            Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
+
+            // Establish the connection
+            try (Connection connection = DriverManager.getConnection(connectionUrl)) {
+                System.out.println("Connected successfully using Kerberos authentication.");
+
+                // Perform a simple query
+                try (Statement statement = connection.createStatement();
+                     ResultSet resultSet = statement.executeQuery("SELECT * from EmployeesDB.dbo.EmployeesTable")) {
+
+                    ResultSetMetaData metaData = resultSet.getMetaData();
+                    int columnCount = metaData.getColumnCount();
+
+                    String[] columns = new String[columnCount];
+                    for (int i = 0; i < columnCount; i++) {
+                        columns[i] = metaData.getColumnName(i + 1);
+                    }
+                    printRow(columns);
+
+                    // Display data rows
+                    while (resultSet.next()) {
+                        String[] row = new String[columnCount];
+                        for (int i = 0; i < columnCount; i++) {
+                            row[i] = resultSet.getString(i + 1);
+                        }
+                        printRow(row);
+                    }
+                }
+            }
+        } catch (ClassNotFoundException e) {
+            System.err.println("Error loading JDBC driver: " + e.getMessage());
+        } catch (SQLException e) {
+            System.err.println("Error connecting to the database: " + e.getMessage());
+        }
+    }
+
+
+    private static void printRow(String[] row) {
+        System.out.println("+---------------------------".repeat(row.length) + "+");
+        for (String col : row) {
+            System.out.printf("| %-25s ", col != null ? col : "NULL");
+        }
+        System.out.println("|");
+    }
+}