Added automatic detection of REALM in SPN needed for Cross Domain authentication.

src/main/java/com/microsoft/sqlserver/jdbc/KerbAuthentication.java

@@ -8,15 +8,22 @@
 
 package com.microsoft.sqlserver.jdbc;
 
+import java.lang.reflect.Method;
 import java.net.IDN;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
 import java.security.AccessControlContext;
 import java.security.AccessController;
 import java.security.PrivilegedActionException;
 import java.security.PrivilegedExceptionAction;
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Level;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
+import javax.naming.NamingException;
 import javax.security.auth.Subject;
 import javax.security.auth.login.AppConfigurationEntry;
 import javax.security.auth.login.Configuration;
@@ -30,6 +37,8 @@
 import org.ietf.jgss.GSSName;
 import org.ietf.jgss.Oid;
 
+import com.microsoft.sqlserver.jdbc.dns.DNSKerberosLocator;
+
 /**
  * KerbAuthentication for int auth.
  */
@@ -247,6 +256,7 @@ private String makeSpn(String server,
         // Get user provided SPN string; if not provided then build the generic one
         String userSuppliedServerSpn = con.activeConnectionProperties.getProperty(SQLServerDriverStringProperty.SERVER_SPN.toString());
 
+        String spn;
         if (null != userSuppliedServerSpn) {
             // serverNameAsACE is true, translate the user supplied serverSPN to ASCII
             if (con.serverNameAsACE()) {
@@ -260,6 +270,152 @@ private String makeSpn(String server,
         else {
             spn = makeSpn(address, port);
         }
+        this.spn = enrichSpnWithRealm(spn, null == userSuppliedServerSpn);
+        if (!this.spn.equals(spn) && authLogger.isLoggable(Level.FINER)){
+            authLogger.finer(toString() + "SPN enriched: " + spn + " := " + this.spn);
+        }
+	}
+
+    private static final Pattern SPN_PATTERN = Pattern.compile("MSSQLSvc/(.*):([^:@]+)(@.+)?", Pattern.CASE_INSENSITIVE);
+
+    private String enrichSpnWithRealm(String spn,
+            boolean allowHostnameCanonicalization) {
+        if (spn == null) {
+            return spn;
+        }
+        Matcher m = SPN_PATTERN.matcher(spn);
+        if (!m.matches()) {
+            return spn;
+        }
+        if (m.group(3) != null) {
+            // Realm is already present, no need to enrich, the job has already been done
+            return spn;
+        }
+        String dnsName = m.group(1);
+        String portOrInstance = m.group(2);
+        RealmValidator realmValidator = getRealmValidator(dnsName);
+        String realm = findRealmFromHostname(realmValidator, dnsName);
+        if (realm == null && allowHostnameCanonicalization) {
+            // We failed, try with canonical host name to find a better match
+            try {
+                String canonicalHostName = InetAddress.getByName(dnsName).getCanonicalHostName();
+                realm = findRealmFromHostname(realmValidator, canonicalHostName);
+                // Since we have a match, our hostname is the correct one (for instance of server
+                // name was an IP), so we override dnsName as well
+                dnsName = canonicalHostName;
+            }
+            catch (UnknownHostException cannotCanonicalize) {
+                // ignored, but we are in a bad shape
+            }
+        }
+        if (realm == null) {
+            return spn;
+        }
+        else {
+            StringBuilder sb = new StringBuilder("MSSQLSvc/");
+            sb.append(dnsName).append(":").append(portOrInstance).append("@").append(realm.toUpperCase(Locale.ENGLISH));
+            return sb.toString();
+        }
+    }
+
+    private static RealmValidator validator;
+
+    /**
+     * Find a suitable way of validating a REALM for given JVM.
+     *
+     * @param hostnameToTest
+     *            an example hostname we are gonna use to test our realm validator.
+     * @return a not null realm Validator.
+     */
+    static RealmValidator getRealmValidator(String hostnameToTest) {
+        if (validator != null) {
+            return validator;
+        }
+        // JVM Specific, here Sun/Oracle JVM
+        try {
+            Class<?> clz = Class.forName("sun.security.krb5.Config");
+            Method getInstance = clz.getMethod("getInstance", new Class[0]);
+            final Method getKDCList = clz.getMethod("getKDCList", new Class[] {String.class});
+            final Object instance = getInstance.invoke(null);
+            RealmValidator oracleRealmValidator = new RealmValidator() {
+
+                @Override
+                public boolean isRealmValid(String realm) {
+                    try {
+                        Object ret = getKDCList.invoke(instance, realm);
+                        return ret != null;
+                    }
+                    catch (Exception err) {
+                        return false;
+                    }
+                }
+            };
+            validator = oracleRealmValidator;
+            // As explained here: https://github.com/Microsoft/mssql-jdbc/pull/40#issuecomment-281509304
+            // The default Oracle Resolution mechanism is not bulletproof
+            // If it resolves a crappy name, drop it.
+            if (!validator.isRealmValid("this.might.not.exist." + hostnameToTest)) {
+                // Our realm validator is well working, return it
+                authLogger.fine("Kerberos Realm Validator: Using Built-in Oracle Realm Validation method.");
+                return oracleRealmValidator;
+            }
+            authLogger.fine("Kerberos Realm Validator: Detected buggy Oracle Realm Validator, using DNSKerberosLocator.");
+        }
+        catch (ReflectiveOperationException notTheRightJVMException) {
+            // Ignored, we simply are not using the right JVM
+            authLogger.fine("Kerberos Realm Validator: No Oracle Realm Validator Available, using DNSKerberosLocator.");
+        }
+        // No implementation found, default one, not any realm is valid
+        validator = new RealmValidator() {
+            @Override
+            public boolean isRealmValid(String realm) {
+                try {
+                    return DNSKerberosLocator.isRealmValid(realm);
+                }
+                catch (NamingException err) {
+                    return false;
+                }
+            }
+        };
+        return validator;
+    }
+
+    /**
+     * Try to find a REALM in the different parts of a host name.
+     *
+     * @param realmValidator
+     *            a function that return true if REALM is valid and exists
+     * @param hostname
+     *            the name we are looking a REALM for
+     * @return the realm if found, null otherwise
+     */
+    private String findRealmFromHostname(RealmValidator realmValidator,
+            String hostname) {
+        if (hostname == null) {
+            return null;
+        }
+        int index = 0;
+        while (index != -1 && index < hostname.length() - 2) {
+            String realm = hostname.substring(index);
+            if (authLogger.isLoggable(Level.FINEST)) {
+                authLogger.finest(toString() + " looking up REALM candidate " + realm);
+            }
+            if (realmValidator.isRealmValid(realm)) {
+                return realm.toUpperCase();
+            }
+            index = hostname.indexOf(".", index + 1);
+            if (index != -1) {
+                index = index + 1;
+            }
+        }
+        return null;
+    }
+
+    /**
+     * JVM Specific implementation to decide whether a realm is valid or not
+     */
+    interface RealmValidator {
+        boolean isRealmValid(String realm);
     }
 
     byte[] GenerateClientContext(byte[] pin,

src/main/java/com/microsoft/sqlserver/jdbc/dns/DNSKerberosLocator.java

@@ -0,0 +1,44 @@
+/*
+ * Microsoft JDBC Driver for SQL Server
+ * 
+ * Copyright(c) Microsoft Corporation All rights reserved.
+ * 
+ * This program is made available under the terms of the MIT License. See the LICENSE file in the project root for more information.
+ */
+package com.microsoft.sqlserver.jdbc.dns;
+
+import java.util.Set;
+
+import javax.naming.NameNotFoundException;
+import javax.naming.NamingException;
+
+public final class DNSKerberosLocator {
+
+    private DNSKerberosLocator() {
+    }
+
+    /**
+     * Tells whether a realm is valid.
+     *
+     * @param realmName
+     *            the realm to test
+     * @return true if realm is valid, false otherwise
+     * @throws NamingException
+     *             if DNS failed, so realm existence cannot be determined
+     */
+    public static boolean isRealmValid(String realmName) throws NamingException {
+        if (realmName == null || realmName.length() < 2) {
+            return false;
+        }
+        if (realmName.startsWith(".")) {
+            realmName = realmName.substring(1);
+        }
+        try {
+            Set<DNSRecordSRV> records = DNSUtilities.findSrvRecords("_kerberos._udp." + realmName);
+            return !records.isEmpty();
+        }
+        catch (NameNotFoundException wrongDomainException) {
+            return false;
+        }
+    }
+}