/* GSSManager.java -- manager class for the GSS-API.
   Copyright (C) 2004 Free Software Foundation, Inc.

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   The documentation comments of this class are derived from the text
   of RFC 2853:  Generic Security Service API Version 2: Java Bindings.
   That document is covered under the following license notice:

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package org.ietf.jgss;

import java.security.Provider;
import java.security.Security;

/**
 * <p>The GSSManager class is an abstract class that serves as a factory
 * for three GSS interfaces: {@link GSSName}, {@link GSSCredential}, and
 * {@link GSSContext}. It also provides methods for applications to determine
 * what mechanisms are available from the GSS implementation and what
 * nametypes these mechanisms support. An instance of the default GSSManager
 * subclass may be obtained through the static method {@link #getInstance()},
 * but applications are free to instantiate other subclasses of GSSManager.</p>
 *
 * <p>All but one method in this class are declared abstract. This means
 * that subclasses have to provide the complete implementation for those
 * methods. The only exception to this is the static method {@link
 * #getInstance()} which will have platform specific code to return an
 * instance of the default subclass.</p>
 *
 * <p>Platform providers of GSS are required not to add any constructors to
 * this class, private, public, or protected. This will ensure that all
 * subclasses invoke only the default constructor provided to the base
 * class by the compiler.</p>
 *
 * <p>A subclass extending the GSSManager abstract class may be implemented
 * as a modular provider based layer that utilizes some well known
 * service provider specification. The GSSManager API provides the
 * application with methods to set provider preferences on such an
 * implementation. These methods also allow the implementation to throw
 * a well-defined exception in case provider based configuration is not
 * supported. Applications that expect to be portable should be aware of
 * this and recover cleanly by catching the exception.</p>
 *
 * <p>It is envisioned that there will be three most common ways in which
 * providers will be used:</p>
 *
 * <ol>
 * <li>The application does not care about what provider is used (the
 * default case).</li>
 *
 * <li>The application wants a particular provider to be used
 * preferentially, either for a particular mechanism or all the
 * time, irrespective of mechanism.</li>
 *
 * <li>The application wants to use the locally configured providers
 * as far as possible but if support is missing for one or more
 * mechanisms then it wants to fall back on its own provider.</li>
 * </ol>
 *
 * <p>The GSSManager class has two methods that enable these modes of
 * usage: {@link #addProviderAtFront(java.security.Provider,org.ietf.jgss.Oid)}
 * and {@link #addProviderAtEnd(java.security.Provider,org.ietf.jgss.Oid)}.
 * These methods have the effect of creating an ordered list of
 * (<i>provider</i>, <i>oid</i>) pairs where each pair indicates a preference
 * of provider for a given oid.</p>
 *
 * <p>The use of these methods does not require any knowledge of whatever
 * service provider specification the GSSManager subclass follows. It is
 * hoped that these methods will serve the needs of most applications.
 * Additional methods may be added to an extended GSSManager that could
 * be part of a service provider specification that is standardized
 * later.</p>
 *
 * <h3>Example Code</h3>
 *
 * <pre>
GSSManager mgr = GSSManager.getInstance();

// What mechs are available to us?
Oid[] supportedMechs = mgr.getMechs();

// Set a preference for the provider to be used when support is needed
// for the mechanisms "1.2.840.113554.1.2.2" and "1.3.6.1.5.5.1.1".

Oid krb = new Oid("1.2.840.113554.1.2.2");
Oid spkm1 = new Oid("1.3.6.1.5.5.1.1");

Provider p = (Provider) (new com.foo.security.Provider());

mgr.addProviderAtFront(p, krb);
mgr.addProviderAtFront(p, spkm1);

// What name types does this spkm implementation support?
Oid[] nameTypes = mgr.getNamesForMech(spkm1);
</pre>
 */
public abstract class GSSManager
{

  // Constructor.
  // -------------------------------------------------------------------------

  public GSSManager()
  {
  }

  // Class method.
  // -------------------------------------------------------------------------

  /**
   * Returns the default GSSManager implementation.
   *
   * @return The default GSSManager implementation.
   */
  public static synchronized GSSManager getInstance()
  {
    String impl = Security.getProperty("org.ietf.jgss.GSSManager");
    if (impl == null)
      impl = "gnu.crypto.gssapi.GSSManagerImpl";
    try
      {
        ClassLoader loader = GSSManager.class.getClassLoader();
        if (loader == null)
          loader = ClassLoader.getSystemClassLoader();
        Class<?> c = loader.loadClass(impl);
        return (GSSManager) c.newInstance();
      }
    catch (Exception x)
      {
        throw new RuntimeException(x.toString());
      }
  }

  // Abstract methods.
  // -------------------------------------------------------------------------

  /**
   * <p>This method is used to indicate to the GSSManager that the
   * application would like a particular provider to be used if no other
   * provider can be found that supports the given mechanism. When a value
   * of null is used instead of an Oid for the mechanism, the GSSManager
   * must use the indicated provider for any mechanism.</p>
   *
   * <p>Calling this method repeatedly preserves the older settings but
   * raises them above newer ones in preference thus forming an ordered
   * list of providers and Oid pairs that grows at the bottom. Thus the
   * older provider settings will be utilized first before this one is.</p>
   *
   * <p>If there are any previously existing preferences that conflict with
   * the preference being set here, then the GSSManager should ignore this
   * request.</p>
   *
   * <p>If the GSSManager implementation does not support an SPI with a
   * pluggable provider architecture it should throw a GSSException with
   * the status code {@link GSSException#UNAVAILABLE} to indicate that the
   * operation is unavailable.</p>
   *
   * @param p    The provider instance that should be used whenever
   *             support is needed for <i>mech</i>.
   * @param mech The mechanism for which the provider is being set.
   * @throws GSSException If this service is unavailable.
   */
  public abstract void addProviderAtEnd(Provider p, Oid mech)
    throws GSSException;

  /**
   * <p>This method is used to indicate to the GSSManager that the
   * application would like a particular provider to be used ahead of all
   * others when support is desired for the given mechanism. When a value
   * of null is used instead of an Oid for the mechanism, the GSSManager
   * must use the indicated provider ahead of all others no matter what
   * the mechanism is. Only when the indicated provider does not support
   * the needed mechanism should the GSSManager move on to a different
   * provider.</p>
   *
   * <p>Calling this method repeatedly preserves the older settings but
   * lowers them in preference thus forming an ordered list of provider
   * and Oid pairs that grows at the top.</p>
   *
   * <p>Calling addProviderAtFront with a null Oid will remove all previous
   * preferences that were set for this provider in the GSSManager
   * instance. Calling addProviderAtFront with a non-null Oid will remove
   * any previous preference that was set using this mechanism and this
   * provider together.</p>
   *
   * <p>If the GSSManager implementation does not support an SPI with a
   * pluggable provider architecture it should throw a GSSException with
   * the status code {@link GSSException#UNAVAILABLE} to indicate that the
   * operation is unavailable.</p>
   *
   * @param p    The provider instance that should be used whenever
   *             support is needed for <i>mech</i>.
   * @param mech The mechanism for which the provider is being set.
   * @throws GSSException If this service is unavailable.
   */
  public abstract void addProviderAtFront(Provider p, Oid mech)
    throws GSSException;

  /**
   * Factory method for creating a previously exported context.  The
   * context properties will be determined from the input token and can't
   * be modified through the set methods.
   *
   * @param interProcessToken The token previously emitted from the
   *                          export method.
   * @return The context.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSContext createContext(byte[] interProcessToken)
    throws GSSException;

  /**
   * Factory method for creating a context on the acceptor' side.  The
   * context's properties will be determined from the input token supplied
   * to the accept method.
   *
   * @param myCred Credentials for the acceptor.  Use <code>null</code> to
   *               act as a default acceptor principal.
   * @return The context.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSContext createContext(GSSCredential myCred)
    throws GSSException;

  /**
   * Factory method for creating a context on the initiator's side.
   * Context flags may be modified through the mutator methods prior to
   * calling {@link
   * GSSContext#initSecContext(java.io.InputStream,java.io.OutputStream)}.
   *
   * @param peer     Name of the target peer.
   * @param mech     Oid of the desired mechanism.  Use <code>null</code>
   *                 to request default mechanism.
   * @param myCred   Credentials of the initiator.  Use <code>null</code>
   *                 default initiator principal.
   * @param lifetime The request lifetime, in seconds, for the context.
   *                 Use {@link GSSContext#INDEFINITE_LIFETIME} and
   *                 {@link GSSContext#DEFAULT_LIFETIME} to request
   *                 indefinite or default context lifetime.
   * @return The context.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSContext createContext(GSSName peer, Oid mech,
                                           GSSCredential myCred, int lifetime)
    throws GSSException;

  /**
   * Factory method for acquiring default credentials.  This will cause
   * the GSS-API to use system specific defaults for the set of
   * mechanisms, name, and a DEFAULT lifetime.
   *
   * @param usage The intended usage for this credential object.  The
   *              value of this parameter must be one of:
   *              {@link GSSCredential#ACCEPT_AND_INITIATE},
   *              {@link GSSCredential#ACCEPT_ONLY},
   *              {@link GSSCredential#INITIATE_ONLY}.
   * @return The credential.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSCredential createCredential(int usage) throws GSSException;

  /**
   * Factory method for acquiring a single mechanism credential.
   *
   * @param aName    Name of the principal for whom this credential is to
   *                 be acquired.  Use <code>null</code> to specify the
   *                 default principal.
   * @param lifetime The number of seconds that credentials should remain
   *                 valid.  Use {@link GSSCredential#INDEFINITE_LIFETIME}
   *                 to request that the credentials have the maximum
   *                 permitted lifetime.  Use {@link
   *                 GSSCredential#DEFAULT_LIFETIME} to request default
   *                 credential lifetime.
   * @param mech     The oid of the desired mechanism.  Use <code>null</code>
   *                 to request the default mechanism(s).
   * @param usage    The intended usage for this credential object.  The
   *                 value of this parameter must be one of:
   *                 {@link GSSCredential#ACCEPT_AND_INITIATE},
   *                 {@link GSSCredential#ACCEPT_ONLY},
   *                 {@link GSSCredential#INITIATE_ONLY}.
   * @return The credential.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSCredential createCredential(GSSName aName, int lifetime,
                                                 Oid mech, int usage)
    throws GSSException;

  /**
   * Factory method for acquiring credentials over a set of mechanisms.
   * Acquires credentials for each of the mechanisms specified in the
   * array called mechs.  To determine the list of mechanisms' for which
   * the acquisition of credentials succeeded, the caller should use the
   * {@link GSSCredential#getMechs()} method.
   *
   * @param aName    Name of the principal for whom this credential is to
   *                 be acquired.  Use <code>null</code> to specify the
   *                 default principal.
   * @param lifetime The number of seconds that credentials should remain
   *                 valid.  Use {@link GSSCredential#INDEFINITE_LIFETIME}
   *                 to request that the credentials have the maximum
   *                 permitted lifetime.  Use {@link
   *                 GSSCredential#DEFAULT_LIFETIME} to request default
   *                 credential lifetime.
   * @param mechs    The array of mechanisms over which the credential is
   *                 to be acquired.  Use <code>null</code> for requesting
   *                 a system specific default set of mechanisms.
   * @param usage    The intended usage for this credential object.  The
   *                 value of this parameter must be one of:
   *                 {@link GSSCredential#ACCEPT_AND_INITIATE},
   *                 {@link GSSCredential#ACCEPT_ONLY},
   *                 {@link GSSCredential#INITIATE_ONLY}.
   * @return The credential.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSCredential createCredential(GSSName aName, int lifetime,
                                                 Oid[] mechs, int usage)
    throws GSSException;

  /**
   * Factory method to convert a contiguous byte array containing a name
   * from the specified namespace to a {@link GSSName} object.  In general,
   * the {@link GSSName} object created will not be an MN; two examples that
   * are exceptions to this are when the namespace type parameter indicates
   * {@link GSSName#NT_EXPORT_NAME} or when the GSS-API implementation is not
   * multi-mechanism.
   *
   * @param name     The byte array containing the name to create.
   * @param nameType The Oid specifying the namespace of the name supplied
   *                 in the byte array.  Note that nameType serves to
   *                 describe and qualify the interpretation of the input
   *                 name byte array, it does not necessarily imply a type
   *                 for the output GSSName implementation. "null" value
   *                 can be used to specify that a mechanism specific
   *                 default syntax should be assumed by each mechanism
   *                 that examines the byte array.
   * @return The name.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSName createName(byte[] name, Oid nameType)
    throws GSSException;

  /**
   * Factory method to convert a contiguous byte array containing a name
   * from the specified namespace to a GSSName object that is an MN.  In
   * other words, this method is a utility that does the equivalent of two
   * steps: {@link #createName(byte[],org.ietf.jgss.Oid)} and then also
   * {@link GSSName#canonicalize(org.ietf.jgss.Oid)}.
   *
   * @param name     The byte array representing the name to create.
   * @param nameType The Oid specifying the namespace of the name supplied
   *                 in the byte array.  Note that nameType serves to
   *                 describe and qualify the interpretation of the input
   *                 name byte array, it does not necessarily imply a type
   *                 for the output GSSName implementation. "null" value
   *                 can be used to specify that a mechanism specific
   *                 default syntax should be assumed by each mechanism
   *                 that examines the byte array.
   * @param mech     Oid specifying the mechanism for which this name
   *                 should be created.
   * @return The name.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSName createName(byte[] name, Oid nameType, Oid mech)
    throws GSSException;

  /**
   * Factory method to convert a contiguous string name from the specified
   * namespace to a {@link GSSName} object.  In general, the {@link GSSName}
   * object created will not be an MN; two examples that are exceptions to
   * this are when the namespace type parameter indicates {@link
   * GSSName#NT_EXPORT_NAME} or when the GSS-API implementation is not
   * multi-mechanism.
   *
   * @param nameStr  The string representing a printable form of the name
   *                 to create.
   * @param nameType The Oid specifying the namespace of the printable name
   *                 supplied. Note that nameType serves to describe and
   *                 qualify the interpretation of the input nameStr, it
   *                 does not necessarily imply a type for the output
   *                 GSSName implementation. "null" value can be used to
   *                 specify that a mechanism specific default printable
   *                 syntax should be assumed by each mechanism that
   *                 examines nameStr.
   * @return The name.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSName createName(String nameStr, Oid nameType)
    throws GSSException;

  /**
   * Factory method to convert a contiguous string name from the specified
   * namespace to an GSSName object that is a mechanism name (MN).  In
   * other words, this method is a utility that does the equivalent of two
   * steps: the {@link #createName(java.lang.String,org.ietf.jgss.Oid)}
   * and then also {@link GSSName#canonicalize(org.ietf.jgss.Oid)}.
   *
   * @param nameStr  The string representing a printable form of the name
   *                 to create.
   * @param nameType The Oid specifying the namespace of the printable name
   *                 supplied.  Note that nameType serves to describe and
   *                 qualify the interpretation of the input nameStr, it
   *                 does not necessarily imply a type for the output
   *                 GSSName implementation. "null" value can be used to
   *                 specify that a mechanism specific default printable
   *                 syntax should be assumed when the mechanism examines
   *                 nameStr.
   * @param mech     Oid specifying the mechanism for which this name
   *                 should be created.
   * @return The name.
   * @throws GSSException If this operation fails.
   */
  public abstract GSSName createName(String nameStr, Oid nameType, Oid mech)
    throws GSSException;

  /**
   * Returns an array of {@link Oid} objects indicating mechanisms available
   * to GSS-API callers.  A <code>null</code> value is returned when no
   * mechanism are available (an example of this would be when mechanism are
   * dynamically configured, and currently no mechanisms are installed).
   *
   * @return The array of available mechanisms, or <code>null</code>.
   */
  public abstract Oid[] getMechs();

  /**
   * Returns an array of {@link Oid} objects corresponding to the mechanisms
   * that support the specific name type. <code>null</code> is returned when
   * no mechanisms are found to support the specified name type.
   *
   * @param name The Oid object for the name type.
   * @return The array of mechanisms, or <code>null</code>.
   */
  public abstract Oid[] getMechsForName(Oid name);

  /**
   * Returns name type Oid's supported by the specified mechanism.
   *
   * @param mechanism The Oid object for the mechanism to query.
   * @return The name type Oid's supported by the mechanism.
   * @throws GSSException If this operation fails.
   */
  public abstract Oid[] getNamesForMech(Oid mechanism) throws GSSException;
}
