001/* Sasl.java --
002   Copyright (C) 2003, 2004, 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package javax.security.sasl;
040
041import java.security.Provider;
042import java.security.Security;
043import java.util.Enumeration;
044import java.util.HashSet;
045import java.util.Iterator;
046import java.util.Map;
047import java.util.Vector;
048
049import javax.security.auth.callback.CallbackHandler;
050
051/**
052 * <p>A static class for creating SASL clients and servers.</p>
053 *
054 * <p>This class defines the policy of how to locate, load, and instantiate SASL
055 * clients and servers.</p>
056 *
057 * <p>For example, an application or library gets a SASL client instance by
058 * doing something like:</p>
059 *
060 * <pre>
061 *SaslClient sc =
062 *      Sasl.createSaslClient(mechanisms, authorizationID, protocol,
063 *                            serverName, props, callbackHandler);
064 * </pre>
065 *
066 * <p>It can then proceed to use the instance to create an authenticated
067 * connection.</p>
068 *
069 * <p>Similarly, a server gets a SASL server instance by using code that looks
070 * as follows:</p>
071 *
072 * <pre>
073 *SaslServer ss =
074 *      Sasl.createSaslServer(mechanism, protocol, serverName, props,
075 *                            callbackHandler);
076 * </pre>
077 *
078 * @since 1.5
079 */
080public class Sasl
081{
082
083  // Constants and variables
084  // -------------------------------------------------------------------------
085
086  /**
087   * <p>The name of a property that specifies the quality-of-protection to use.
088   * The property contains a comma-separated, ordered list of quality-of-
089   * protection values that the client or server is willing to support. A qop
090   * value is one of:</p>
091   *
092   * <ul>
093   *    <li><code>"auth"</code> - authentication only,</li>
094   *    <li><code>"auth-int"</code> - authentication plus integrity
095   *    protection,</li>
096   *    <li><code>"auth-conf"</code> - authentication plus integrity and
097   *    confidentiality protection.</li>
098   * </ul>
099   *
100   * <p>The order of the list specifies the preference order of the client or
101   * server.</p>
102   *
103   * <p>If this property is absent, the default qop is <code>"auth"</code>.</p>
104   *
105   * <p>The value of this constant is <code>"javax.security.sasl.qop"</code>.</p>
106   */
107  public static final String QOP = "javax.security.sasl.qop";
108
109  /**
110   * <p>The name of a property that specifies the cipher strength to use. The
111   * property contains a comma-separated, ordered list of cipher strength
112   * values that the client or server is willing to support. A strength value
113   * is one of:</p>
114   *
115   * <ul>
116   *    <li><code>"low"</code>,</li>
117   *    <li><code>"medium"</code>,</li>
118   *    <li><code>"high"</code>.</li>
119   * </ul>
120   *
121   * <p>The order of the list specifies the preference order of the client or
122   * server. An implementation should allow configuration of the meaning of
123   * these values. An application may use the Java Cryptography Extension (JCE)
124   * with JCE-aware mechanisms to control the selection of cipher suites that
125   * match the strength values.</p>
126   *
127   * <p>If this property is absent, the default strength is
128   * <code>"high,medium,low"</code>.</p>
129   *
130   * <p>The value of this constant is <code>"javax.security.sasl.strength"</code>.
131   * </p>
132   */
133  public static final String STRENGTH = "javax.security.sasl.strength";
134
135  /**
136   * <p>The name of a property that specifies whether the server must authenticate
137   * to the client. The property contains <code>"true"</code> if the server
138   * must authenticate the to client; <code>"false"</code> otherwise. The
139   * default is <code>"false"</code>.</p>
140   *
141   * <p>The value of this constant is
142   * <code>"javax.security.sasl.server.authentication"</code>.</p>
143   */
144  public static final String SERVER_AUTH = "javax.security.sasl.server.authentication";
145
146  /**
147   * <p>The name of a property that specifies the maximum size of the receive
148   * buffer in bytes of {@link SaslClient}/{@link SaslServer}. The property
149   * contains the string representation of an integer.</p>
150   *
151   * <p>If this property is absent, the default size is defined by the
152   * mechanism.</p>
153   *
154   * <p>The value of this constant is <code>"javax.security.sasl.maxbuffer"</code>.
155   * </p>
156   */
157  public static final String MAX_BUFFER = "javax.security.sasl.maxbuffer";
158
159  /**
160   * <p>The name of a property that specifies the maximum size of the raw send
161   * buffer in bytes of {@link SaslClient}/{@link SaslServer}. The property
162   * contains the string representation of an integer. The value of this
163   * property is negotiated between the client and server during the
164   * authentication exchange.</p>
165   *
166   * <p>The value of this constant is <code>"javax.security.sasl.rawsendsize"</code>.
167   * </p>
168   */
169  public static final String RAW_SEND_SIZE = "javax.security.sasl.rawsendsize";
170
171  /**
172   * <p>The name of a property that specifies whether mechanisms susceptible
173   * to simple plain passive attacks (e.g., "PLAIN") are not permitted. The
174   * property contains <code>"true"</code> if such mechanisms are not
175   * permitted; <code>"false"</code> if such mechanisms are permitted. The
176   * default is <code>"false"</code>.</p>
177   *
178   * <p>The value of this constant is <code>"javax.security.sasl.policy.noplaintext"</code>.
179   * </p>
180   */
181  public static final String POLICY_NOPLAINTEXT = "javax.security.sasl.policy.noplaintext";
182
183  /**
184   * <p>The name of a property that specifies whether mechanisms susceptible to
185   * active (non-dictionary) attacks are not permitted. The property contains
186   * <code>"true"</code> if mechanisms susceptible to active attacks are not
187   * permitted; <code>"false"</code> if such mechanisms are permitted. The
188   * default is <code>"false"</code>.</p>
189   *
190   * <p>The value of this constant is <code>"javax.security.sasl.policy.noactive"</code>.
191   * </p>
192   */
193  public static final String POLICY_NOACTIVE = "javax.security.sasl.policy.noactive";
194
195  /**
196   * <p>The name of a property that specifies whether mechanisms susceptible to
197   * passive dictionary attacks are not permitted. The property contains
198   * <code>"true"</code> if mechanisms susceptible to dictionary attacks are
199   * not permitted; <code>"false"</code> if such mechanisms are permitted. The
200   * default is <code>"false"</code>.</p>
201   *
202   * <p>The value of this constant is <code>"javax.security.sasl.policy.nodictionary"</code>.
203   * </p>
204   */
205  public static final String POLICY_NODICTIONARY = "javax.security.sasl.policy.nodictionary";
206
207  /**
208   * <p>The name of a property that specifies whether mechanisms that accept
209   * anonymous login are not permitted. The property contains <code>"true"</code>
210   * if mechanisms that accept anonymous login are not permitted; <code>"false"
211   * </code> if such mechanisms are permitted. The default is <code>"false"</code>.
212   * </p>
213   *
214   * <p>The value of this constant is <code>"javax.security.sasl.policy.noanonymous"</code>.
215   * </p>
216   */
217  public static final String POLICY_NOANONYMOUS = "javax.security.sasl.policy.noanonymous";
218
219  /**
220   * The name of a property that specifies whether mechanisms that implement
221   * forward secrecy between sessions are required. Forward secrecy means that
222   * breaking into one session will not automatically provide information for
223   * breaking into future sessions. The property contains <code>"true"</code>
224   * if mechanisms that implement forward secrecy between sessions are
225   * required; <code>"false"</code> if such mechanisms are not required. The
226   * default is <code>"false"</code>.
227   *
228   * <p>The value of this constant is <code>"javax.security.sasl.policy.forward"</code>.
229   * </p>
230   */
231  public static final String POLICY_FORWARD_SECRECY = "javax.security.sasl.policy.forward";
232
233  /**
234   * The name of a property that specifies whether mechanisms that pass client
235   * credentials are required. The property contains <code>"true"</code> if
236   * mechanisms that pass client credentials are required; <code>"false"</code>
237   * if such mechanisms are not required. The default is <code>"false"</code>.
238   *
239   * <p>The value of this constant is <code>"javax.security.sasl.policy.credentials"</code>.
240   * </p>
241   */
242  public static final String POLICY_PASS_CREDENTIALS = "javax.security.sasl.policy.credentials";
243
244  /**
245   * <p>The name of a property that specifies whether to reuse previously
246   * authenticated session information. The property contains <code>"true"</code>
247   * if the mechanism implementation may attempt to reuse previously
248   * authenticated session information; it contains <code>"false"</code> if the
249   * implementation must not reuse previously authenticated session information.
250   * A setting of <code>"true"</code> serves only as a hint; it does not
251   * necessarily entail actual reuse because reuse might not be possible due to
252   * a number of reasons, including, but not limited to, lack of mechanism
253   * support for reuse, expiration of reusable information, and the peer's
254   * refusal to support reuse. The property's default value is <code>"false"</code>.
255   * </p>
256   *
257   * <p>The value of this constant is <code>"javax.security.sasl.reuse"</code>.
258   * Note that all other parameters and properties required to create a SASL
259   * client/server instance must be provided regardless of whether this
260   * property has been supplied. That is, you cannot supply any less
261   * information in anticipation of reuse. Mechanism implementations that
262   * support reuse might allow customization of its implementation for factors
263   * such as cache size, timeouts, and criteria for reuseability. Such
264   * customizations are implementation-dependent.</p>
265   */
266  public static final String REUSE = "javax.security.sasl.reuse";
267
268  /**
269   * <p>The name of a property which specifies the credentials to use.
270   * The value of the property is a mechanism-specific object which can
271   * be used to supply credentials to a mechanism which provides delegated
272   * authentication.</p>
273   *
274   * <p>The value of this constant is <code>"javax.security.sasl.credentials"</code>.</p>
275   */
276  public static final String CREDENTIALS = "javax.security.sasl.credentials";
277
278  private static final String CLIENT_FACTORY_SVC = "SaslClientFactory.";
279  private static final String SERVER_FACTORY_SVC = "SaslServerFactory.";
280  private static final String ALIAS = "Alg.Alias.";
281
282  // Constructor(s)
283  // -------------------------------------------------------------------------
284
285  private Sasl()
286  {
287    super();
288  }
289
290  // Class methods
291  // -------------------------------------------------------------------------
292
293  /**
294   * Creates a {@link SaslClient} for the specified mechanism.
295   *
296   * <p>This method uses the JCA Security Provider Framework, described in the
297   * "Java Cryptography Architecture API Specification &amp; Reference", for
298   * locating and selecting a {@link SaslClient} implementation.</p>
299   *
300   * <p>First, it obtains an ordered list of {@link SaslClientFactory}
301   * instances from the registered security providers for the
302   * <code>"SaslClientFactory"</code> service and the specified mechanism. It
303   * then invokes <code>createSaslClient()</code> on each factory instance on
304   * the list until one produces a non-null {@link SaslClient} instance. It
305   * returns the non-null {@link SaslClient} instance, or <code>null</code> if
306   * the search fails to produce a non-null {@link SaslClient} instance.</p>
307   *
308   * <p>A security provider for <code>SaslClientFactory</code> registers with
309   * the JCA Security Provider Framework keys of the form:</p>
310   *
311   * <pre>
312   *    SaslClientFactory.mechanism_name
313   * </pre>
314   *
315   * <p>and values that are class names of implementations of {@link
316   * SaslClientFactory}.</p>
317   *
318   * <p>For example, a provider that contains a factory class,
319   * <code>com.wiz.sasl.digest.ClientFactory</code>, that supports the
320   * <code>"DIGEST-MD5"</code> mechanism would register the following entry
321   * with the JCA:</p>
322   *
323   * <pre>
324   *    SaslClientFactory.DIGEST-MD5     com.wiz.sasl.digest.ClientFactory
325   * </pre>
326   *
327   * <p>See the "Java Cryptography Architecture API Specification &amp;
328   * Reference" for information about how to install and configure security
329   * service providers.</p>
330   *
331   * @param mechanisms the non-null list of mechanism names to try. Each is the
332   * IANA-registered name of a SASL mechanism. (e.g. "GSSAPI", "CRAM-MD5").
333   * @param authorizationID the possibly <code>null</code> protocol-dependent
334   * identification to be used for authorization. If <code>null</code> or
335   * empty, the server derives an authorization ID from the client's
336   * authentication credentials. When the SASL authentication completes
337   * successfully, the specified entity is granted access.
338   * @param protocol the non-null string name of the protocol for which the
339   * authentication is being performed (e.g. "ldap").
340   * @param serverName the non-null fully-qualified host name of the server to
341   * authenticate to.
342   * @param props the possibly null set of properties used to select the SASL
343   * mechanism and to configure the authentication exchange of the selected
344   * mechanism. For example, if props contains the {@link Sasl#POLICY_NOPLAINTEXT}
345   * property with the value <code>"true"</code>, then the selected SASL
346   * mechanism must not be susceptible to simple plain passive attacks. In
347   * addition to the standard properties declared in this class, other,
348   * possibly mechanism-specific, properties can be included. Properties not
349   * relevant to the selected mechanism are ignored.
350   * @param cbh the possibly <code>null</code> callback handler to used by the
351   * SASL mechanisms to get further information from the application/library to
352   * complete the authentication. For example, a SASL mechanism might require
353   * the authentication ID, password and realm from the caller. The
354   * authentication ID is requested by using a
355   * {@link javax.security.auth.callback.NameCallback}. The password is
356   * requested by using a {@link javax.security.auth.callback.PasswordCallback}.
357   * The realm is requested by using a {@link RealmChoiceCallback} if there is
358   * a list of realms to choose from, and by using a {@link RealmCallback} if
359   * the realm must be entered.
360   * @return a possibly <code>null</code> {@link SaslClient} created using the
361   * parameters supplied. If <code>null</code>, the method could not find a
362   * {@link SaslClientFactory} that will produce one.
363   * @throws SaslException if a {@link SaslClient} cannot be created because
364   * of an error.
365   */
366  public static SaslClient createSaslClient(String[] mechanisms,
367                                            String authorizationID,
368                                            String protocol,
369                                            String serverName,
370                                            Map<String, ?> props,
371                                            CallbackHandler cbh)
372    throws SaslException
373  {
374    if (mechanisms == null)
375      {
376        return null;
377      }
378    Provider[] providers = Security.getProviders();
379    if (providers == null || providers.length == 0)
380      {
381        return null;
382      }
383
384    SaslClient result = null;
385    SaslClientFactory factory = null;
386    String m, clazz = null, upper, alias;
387    int j;
388    Provider p;
389    for (int i = 0; i < mechanisms.length; i++)
390      {
391        m = mechanisms[i];
392        if (m == null)
393          continue;
394        for (j = 0; j < providers.length; j++)
395          {
396            p = providers[j];
397            if (p != null)
398              {
399                // try the name as is
400                clazz = p.getProperty(CLIENT_FACTORY_SVC + m);
401                if (clazz == null) // try all uppercase
402                  {
403                    upper = m.toUpperCase();
404                    clazz = p.getProperty(CLIENT_FACTORY_SVC + upper);
405                    if (clazz == null) // try if it's an alias
406                      {
407                        alias = p.getProperty(ALIAS + CLIENT_FACTORY_SVC + m);
408                        if (alias == null) // try all-uppercase alias name
409                          {
410                            alias = p.getProperty(ALIAS + CLIENT_FACTORY_SVC + upper);
411                            if (alias == null) // spit the dummy
412                              continue;
413                          }
414                        clazz = p.getProperty(CLIENT_FACTORY_SVC + alias);
415                      }
416                  }
417                if (clazz == null)
418                  continue;
419                else
420                  clazz = clazz.trim();
421              }
422
423            try
424              {
425                result = null;
426                factory = (SaslClientFactory) Class.forName(clazz).newInstance();
427                result = factory.createSaslClient(mechanisms, authorizationID,
428                                                  protocol, serverName, props, cbh);
429              }
430            catch (ClassCastException ignored) // ignore instantiation exceptions
431              {
432              }
433            catch (ClassNotFoundException ignored)
434              {
435              }
436            catch (InstantiationException ignored)
437              {
438              }
439            catch (IllegalAccessException ignored)
440              {
441              }
442            if (result != null)
443              return result;
444          }
445      }
446    return null;
447  }
448
449  /**
450   * Gets an enumeration of known factories for producing a {@link SaslClient}
451   * instance. This method uses the same sources for locating factories as
452   * <code>createSaslClient()</code>.
453   *
454   * @return a non-null {@link Enumeration} of known factories for producing a
455   * {@link SaslClient} instance.
456   * @see #createSaslClient(String[],String,String,String,Map,CallbackHandler)
457   */
458  public static Enumeration<SaslClientFactory> getSaslClientFactories()
459  {
460    Vector result = new Vector();
461    HashSet names = new HashSet();
462    Provider[] providers = Security.getProviders();
463    Iterator it;
464    if (providers != null)
465      {
466        Provider p;
467        String key;
468        for (int i = 0; i < providers.length; i++)
469          {
470            p = providers[i];
471            for (it = p.keySet().iterator(); it.hasNext(); )
472              {
473                key = (String) it.next();
474                // add key's binding (a) it is a class of a client factory,
475                // and (b) the key does not include blanks
476                if (key.startsWith(CLIENT_FACTORY_SVC) && key.indexOf(" ") == -1)
477                  {
478                    names.add(p.getProperty(key));
479                    break;
480                  }
481              }
482          }
483      }
484    // we have the factory class names in names; instantiate and enumerate
485    String c;
486    for (it = names.iterator(); it.hasNext(); )
487      {
488        c = (String) it.next();
489        try
490          {
491            SaslClientFactory f = (SaslClientFactory) Class.forName(c).newInstance();
492            if (f != null)
493              result.add(f);
494          } catch (ClassCastException ignored) { // ignore instantiation exceptions
495          } catch (ClassNotFoundException ignored) {
496          } catch (InstantiationException ignored) {
497          } catch (IllegalAccessException ignored) {
498          }
499      }
500
501    return result.elements();
502  }
503
504  /**
505   * Creates a {@link SaslServer} for the specified mechanism.
506   *
507   * <p>This method uses the JCA Security Provider Framework, described in the
508   * "Java Cryptography Architecture API Specification &amp; Reference", for
509   * locating and selecting a SaslServer implementation.</p>
510   *
511   * <p>First, it obtains an ordered list of {@link SaslServerFactory}
512   * instances from the registered security providers for the
513   * <code>"SaslServerFactory"</code> service and the specified mechanism. It
514   * then invokes <code>createSaslServer()</code> on each factory instance on
515   * the list until one produces a non-null {@link SaslServer} instance. It
516   * returns the non-null {@link SaslServer} instance, or <code>null</code> if
517   * the search fails to produce a non-null {@link SaslServer} instance.</p>
518   *
519   * <p>A security provider for {@link SaslServerFactory} registers with the
520   * JCA Security Provider Framework keys of the form:</p>
521   *
522   * <pre>
523   *    SaslServerFactory.mechanism_name
524   * </pre>
525   *
526   * <p>and values that are class names of implementations of {@link
527   * SaslServerFactory}.</p>
528   *
529   * <p>For example, a provider that contains a factory class,
530   * <code>com.wiz.sasl.digest.ServerFactory</code>, that supports the
531   * <code>"DIGEST-MD5"</code> mechanism would register the following entry
532   * with the JCA:</p>
533   *
534   * <pre>
535   *    SaslServerFactory.DIGEST-MD5     com.wiz.sasl.digest.ServerFactory
536   * </pre>
537   *
538   * <p>See the "Java Cryptography Architecture API Specification &amp;
539   * Reference" for information about how to install and configure security
540   * service providers.</p>
541   *
542   * @param mechanism the non-null mechanism name. It must be an
543   * IANA-registered name of a SASL mechanism. (e.g. "GSSAPI", "CRAM-MD5").
544   * @param protocol the non-null string name of the protocol for which the
545   * authentication is being performed (e.g. "ldap").
546   * @param serverName the non-null fully qualified host name of the server.
547   * @param props the possibly <code>null</code> set of properties used to
548   * select the SASL mechanism and to configure the authentication exchange of
549   * the selected mechanism. For example, if props contains the {@link
550   * Sasl#POLICY_NOPLAINTEXT} property with the value <code>"true"</code>, then
551   * the selected SASL mechanism must not be susceptible to simple plain
552   * passive attacks. In addition to the standard properties declared in this
553   * class, other, possibly mechanism-specific, properties can be included.
554   * Properties not relevant to the selected mechanism are ignored.
555   * @param cbh the possibly <code>null</code> callback handler to used by the
556   * SASL mechanisms to get further information from the application/library to
557   * complete the authentication. For example, a SASL mechanism might require
558   * the authentication ID, password and realm from the caller. The
559   * authentication ID is requested by using a
560   * {@link javax.security.auth.callback.NameCallback}. The password is
561   * requested by using a {@link javax.security.auth.callback.PasswordCallback}.
562   * The realm is requested by using a {@link RealmChoiceCallback} if there is
563   * a list of realms to choose from, and by using a {@link RealmCallback} if
564   * the realm must be entered.
565   * @return a possibly <code>null</code> {@link SaslServer} created using the
566   * parameters supplied. If <code>null</code>, the method cannot find a
567   * {@link SaslServerFactory} instance that will produce one.
568   * @throws SaslException if a {@link SaslServer} instance cannot be created
569   * because of an error.
570   */
571  public static SaslServer createSaslServer(String mechanism, String protocol,
572                                            String serverName,
573                                            Map<String, ?> props,
574                                            CallbackHandler cbh)
575    throws SaslException
576  {
577    if (mechanism == null)
578      return null;
579    Provider[] providers = Security.getProviders();
580    if (providers == null || providers.length == 0)
581      return null;
582
583    SaslServer result = null;
584    SaslServerFactory factory = null;
585    String clazz = null, upper, alias = null;
586    int j;
587    Provider p;
588    for (j = 0; j < providers.length; j++)
589      {
590        p = providers[j];
591        if (p != null)
592          {
593            // try the name as is
594            clazz = p.getProperty(SERVER_FACTORY_SVC + mechanism);
595            if (clazz == null) // try all uppercase
596              {
597                upper = mechanism.toUpperCase();
598                clazz = p.getProperty(SERVER_FACTORY_SVC + upper);
599                if (clazz == null) // try if it's an alias
600                  {
601                    alias = p.getProperty(ALIAS + SERVER_FACTORY_SVC + mechanism);
602                    if (alias == null) // try all-uppercase alias name
603                      {
604                        alias = p.getProperty(ALIAS + SERVER_FACTORY_SVC + upper);
605                        if (alias == null) // spit the dummy
606                          continue;
607                      }
608                  }
609                clazz = p.getProperty(SERVER_FACTORY_SVC + alias);
610              }
611          }
612        if (clazz == null)
613          continue;
614        else
615          clazz = clazz.trim();
616
617        try
618          {
619            result = null;
620            factory = (SaslServerFactory) Class.forName(clazz).newInstance();
621            result =
622              factory.createSaslServer(mechanism, protocol, serverName, props, cbh);
623          }
624        catch (ClassCastException ignored) // ignore instantiation exceptions
625          {
626          }
627        catch (ClassNotFoundException ignored)
628          {
629          }
630        catch (InstantiationException ignored)
631          {
632          }
633        catch (IllegalAccessException ignored)
634          {
635          }
636        if (result != null)
637          return result;
638      }
639    return null;
640  }
641
642  /**
643   * Gets an enumeration of known factories for producing a {@link SaslServer}
644   * instance. This method uses the same sources for locating factories as
645   * <code>createSaslServer()</code>.
646   *
647   * @return a non-null {@link Enumeration} of known factories for producing a
648   * {@link SaslServer} instance.
649   * @see #createSaslServer(String,String,String,Map,CallbackHandler)
650   */
651  public static Enumeration<SaslServerFactory> getSaslServerFactories()
652  {
653    Vector result = new Vector();
654    HashSet names = new HashSet();
655    Provider[] providers = Security.getProviders();
656    Iterator it;
657    if (providers != null)
658      {
659        Provider p;
660        String key;
661        for (int i = 0; i < providers.length; i++)
662          {
663            p = providers[i];
664            for (it = p.keySet().iterator(); it.hasNext(); )
665              {
666                key = (String) it.next();
667                // add key's binding (a) it is a class of a server factory,
668                // and (b) the key does not include blanks
669                if (key.startsWith(SERVER_FACTORY_SVC) && key.indexOf(" ") == -1)
670                  {
671                    names.add(p.getProperty(key));
672                    break;
673                  }
674              }
675          }
676      }
677    // we have the factory class names in names; instantiate and enumerate
678    String c;
679    for (it = names.iterator(); it.hasNext(); )
680      {
681        c = (String) it.next();
682        try
683          {
684            SaslServerFactory f = (SaslServerFactory) Class.forName(c).newInstance();
685            if (f != null)
686              result.add(f);
687          }
688        catch (ClassCastException ignored) // ignore instantiation exceptions
689          {
690          }
691        catch (ClassNotFoundException ignored)
692          {
693          }
694        catch (InstantiationException ignored)
695          {
696          }
697        catch (IllegalAccessException ignored)
698          {
699          }
700      }
701
702    return result.elements();
703  }
704}