/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  package org.apache.shiro.realm.ldap;
  
  import org.apache.shiro.authc.AuthenticationException;
  import org.apache.shiro.authc.AuthenticationInfo;
  import org.apache.shiro.authc.AuthenticationToken;
  import org.apache.shiro.authc.SimpleAuthenticationInfo;
  import org.apache.shiro.authc.credential.AllowAllCredentialsMatcher;
  import org.apache.shiro.authz.AuthorizationException;
  import org.apache.shiro.authz.AuthorizationInfo;
  import org.apache.shiro.ldap.UnsupportedAuthenticationMechanismException;
  import org.apache.shiro.realm.AuthorizingRealm;
  import org.apache.shiro.subject.PrincipalCollection;
  import org.apache.shiro.util.StringUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import javax.naming.AuthenticationNotSupportedException;
  import javax.naming.NamingException;
  import javax.naming.ldap.LdapContext;
  
  /**
   * An LDAP {@link org.apache.shiro.realm.Realm Realm} implementation utilizing Sun's/Oracle's
   * <a href="http://download-llnw.oracle.com/javase/tutorial/jndi/ldap/jndi.html">JNDI API as an LDAP API</a>.  This is
   * Shiro's default implementation for supporting LDAP, as using the JNDI API has been a common approach for Java LDAP
   * support for many years.
   * <p/>
   * This realm implementation and its backing {@link JndiLdapContextFactory} should cover 99% of all Shiro-related LDAP
   * authentication and authorization needs.  However, if it does not suit your needs, you might want to look into
   * creating your own realm using an alternative, perhaps more robust, LDAP communication API, such as the
   * <a href="http://directory.apache.org/api/">Apache LDAP API</a>.
   * <h2>Authentication</h2>
   * During an authentication attempt, if the submitted {@code AuthenticationToken}'s
   * {@link org.apache.shiro.authc.AuthenticationToken#getPrincipal() principal} is a simple username, but the
   * LDAP directory expects a complete User Distinguished Name (User DN) to establish a connection, the
   * {@link #setUserDnTemplate(String) userDnTemplate} property must be configured.  If not configured,
   * the property will pass the simple username directly as the User DN, which is often incorrect in most LDAP
   * environments (maybe Microsoft ActiveDirectory being the exception).
   * <h2>Authorization</h2>
   * By default, authorization is effectively disabled due to the default
   * {@link #doGetAuthorizationInfo(org.apache.shiro.subject.PrincipalCollection)} implementation returning {@code null}.
   * If you wish to perform authorization based on an LDAP schema, you must subclass this one
   * and override that method to reflect your organization's data model.
   * <h2>Configuration</h2>
   * This class primarily provides the {@link #setUserDnTemplate(String) userDnTemplate} property to allow you to specify
   * the your LDAP server's User DN format.  Most other configuration is performed via the nested
   * {@link LdapContextFactory contextFactory} property.
   * <p/>
   * For example, defining this realm in Shiro .ini:
   * <pre>
   * [main]
   * ldapRealm = org.apache.shiro.realm.ldap.DefaultLdapRealm
   * ldapRealm.userDnTemplate = uid={0},ou=users,dc=mycompany,dc=com
   * ldapRealm.contextFactory.url = ldap://ldapHost:389
   * ldapRealm.contextFactory.authenticationMechanism = DIGEST-MD5
   * ldapRealm.contextFactory.environment[some.obscure.jndi.key] = some value
   * ...
   * </pre>
   * The default {@link #setContextFactory contextFactory} instance is a {@link JndiLdapContextFactory}.  See that
   * class's JavaDoc for more information on configuring the LDAP connection as well as specifying JNDI environment
   * properties as necessary.
   *
   * @see JndiLdapContextFactory
   *
   * @since 1.3
   */
  public class DefaultLdapRealm extends AuthorizingRealm {
  
      private static final Logger log = LoggerFactory.getLogger(DefaultLdapRealm.class);
  
      //The zero index currently means nothing, but could be utilized in the future for other substitution techniques.
      private static final String USERDN_SUBSTITUTION_TOKEN = "{0}";
  
      private String userDnPrefix;
      private String userDnSuffix;
  
      /*--------------------------------------------
      |    I N S T A N C E   V A R I A B L E S    |
      ============================================*/
      /**
       * The LdapContextFactory instance used to acquire {@link javax.naming.ldap.LdapContext LdapContext}'s at runtime
       * to acquire connections to the LDAP directory to perform authentication attempts and authorizatino queries.
      */
     private LdapContextFactory contextFactory;
 
     /*--------------------------------------------
     |         C O N S T R U C T O R S           |
     ============================================*/
 
     /**
      * Default no-argument constructor that defaults the internal {@link LdapContextFactory} instance to a
      * {@link JndiLdapContextFactory}.
      */
     public DefaultLdapRealm() {
         //Credentials Matching is not necessary - the LDAP directory will do it automatically:
         setCredentialsMatcher(new AllowAllCredentialsMatcher());
         //Any Object principal and Object credentials may be passed to the LDAP provider, so accept any token:
         setAuthenticationTokenClass(AuthenticationToken.class);
         this.contextFactory = new JndiLdapContextFactory();
     }
 
     /*--------------------------------------------
     |  A C C E S S O R S / M O D I F I E R S    |
     ============================================*/
 
     /**
      * Returns the User DN prefix to use when building a runtime User DN value or {@code null} if no
      * {@link #getUserDnTemplate() userDnTemplate} has been configured.  If configured, this value is the text that
      * occurs before the {@link #USERDN_SUBSTITUTION_TOKEN} in the {@link #getUserDnTemplate() userDnTemplate} value.
      *
      * @return the the User DN prefix to use when building a runtime User DN value or {@code null} if no
      *         {@link #getUserDnTemplate() userDnTemplate} has been configured.
      */
     protected String getUserDnPrefix() {
         return userDnPrefix;
     }
 
     /**
      * Returns the User DN suffix to use when building a runtime User DN value.  or {@code null} if no
      * {@link #getUserDnTemplate() userDnTemplate} has been configured.  If configured, this value is the text that
      * occurs after the {@link #USERDN_SUBSTITUTION_TOKEN} in the {@link #getUserDnTemplate() userDnTemplate} value.
      *
      * @return the User DN suffix to use when building a runtime User DN value or {@code null} if no
      *         {@link #getUserDnTemplate() userDnTemplate} has been configured.
      */
     protected String getUserDnSuffix() {
         return userDnSuffix;
     }
 
     /*--------------------------------------------
     |               M E T H O D S               |
     ============================================*/
 
     /**
      * Sets the User Distinguished Name (DN) template to use when creating User DNs at runtime.  A User DN is an LDAP
      * fully-qualified unique user identifier which is required to establish a connection with the LDAP
      * directory to authenticate users and query for authorization information.
      * <h2>Usage</h2>
      * User DN formats are unique to the LDAP directory's schema, and each environment differs - you will need to
      * specify the format corresponding to your directory.  You do this by specifying the full User DN as normal, but
      * but you use a <b>{@code {0}}</b> placeholder token in the string representing the location where the
      * user's submitted principal (usually a username or uid) will be substituted at runtime.
      * <p/>
      * For example,  if your directory
      * uses an LDAP {@code uid} attribute to represent usernames, the User DN for the {@code jsmith} user may look like
      * this:
      * <p/>
      * <pre>uid=jsmith,ou=users,dc=mycompany,dc=com</pre>
      * <p/>
      * in which case you would set this property with the following template value:
      * <p/>
      * <pre>uid=<b>{0}</b>,ou=users,dc=mycompany,dc=com</pre>
      * <p/>
      * If no template is configured, the raw {@code AuthenticationToken}
      * {@link AuthenticationToken#getPrincipal() principal} will be used as the LDAP principal.  This is likely
      * incorrect as most LDAP directories expect a fully-qualified User DN as opposed to the raw uid or username.  So,
      * ensure you set this property to match your environment!
      *
      * @param template the User Distinguished Name template to use for runtime substitution
      * @throws IllegalArgumentException if the template is null, empty, or does not contain the
      *                                  {@code {0}} substitution token.
      * @see LdapContextFactory#getLdapContext(Object,Object)
      */
     public void setUserDnTemplate(String template) throws IllegalArgumentException {
         if (!StringUtils.hasText(template)) {
             String msg = "User DN template cannot be null or empty.";
             throw new IllegalArgumentException(msg);
         }
         int index = template.indexOf(USERDN_SUBSTITUTION_TOKEN);
         if (index < 0) {
             String msg = "User DN template must contain the '" +
                     USERDN_SUBSTITUTION_TOKEN + "' replacement token to understand where to " +
                     "insert the runtime authentication principal.";
             throw new IllegalArgumentException(msg);
         }
         String prefix = template.substring(0, index);
         String suffix = template.substring(prefix.length() + USERDN_SUBSTITUTION_TOKEN.length());
         if (log.isDebugEnabled()) {
             log.debug("Determined user DN prefix [{}] and suffix [{}]", prefix, suffix);
         }
         this.userDnPrefix = prefix;
         this.userDnSuffix = suffix;
     }
 
     /**
      * Returns the User Distinguished Name (DN) template to use when creating User DNs at runtime - see the
      * {@link #setUserDnTemplate(String) setUserDnTemplate} JavaDoc for a full explanation.
      *
      * @return the User Distinguished Name (DN) template to use when creating User DNs at runtime.
      */
     public String getUserDnTemplate() {
         return getUserDn(USERDN_SUBSTITUTION_TOKEN);
     }
 
     /**
      * Returns the LDAP User Distinguished Name (DN) to use when acquiring an
      * {@link javax.naming.ldap.LdapContext LdapContext} from the {@link LdapContextFactory}.
      * <p/>
      * If the the {@link #getUserDnTemplate() userDnTemplate} property has been set, this implementation will construct
      * the User DN by substituting the specified {@code principal} into the configured template.  If the
      * {@link #getUserDnTemplate() userDnTemplate} has not been set, the method argument will be returned directly
      * (indicating that the submitted authentication token principal <em>is</em> the User DN).
      *
      * @param principal the principal to substitute into the configured {@link #getUserDnTemplate() userDnTemplate}.
      * @return the constructed User DN to use at runtime when acquiring an {@link javax.naming.ldap.LdapContext}.
      * @throws IllegalArgumentException if the method argument is null or empty
      * @throws IllegalStateException    if the {@link #getUserDnTemplate userDnTemplate} has not been set.
      * @see LdapContextFactory#getLdapContext(Object, Object)
      */
     protected String getUserDn(String principal) throws IllegalArgumentException, IllegalStateException {
         if (!StringUtils.hasText(principal)) {
             throw new IllegalArgumentException("User principal cannot be null or empty for User DN construction.");
         }
         String prefix = getUserDnPrefix();
         String suffix = getUserDnSuffix();
         if (prefix == null && suffix == null) {
             log.debug("userDnTemplate property has not been configured, indicating the submitted " +
                     "AuthenticationToken's principal is the same as the User DN.  Returning the method argument " +
                     "as is.");
             return principal;
         }
 
         int prefixLength = prefix != null ? prefix.length() : 0;
         int suffixLength = suffix != null ? suffix.length() : 0;
         StringBuilder sb = new StringBuilder(prefixLength + principal.length() + suffixLength);
         if (prefixLength > 0) {
             sb.append(prefix);
         }
         sb.append(principal);
         if (suffixLength > 0) {
             sb.append(suffix);
         }
         return sb.toString();
     }
 
     /**
      * Sets the LdapContextFactory instance used to acquire connections to the LDAP directory during authentication
      * attempts and authorization queries.  Unless specified otherwise, the default is a {@link JndiLdapContextFactory}
      * instance.
      *
      * @param contextFactory the LdapContextFactory instance used to acquire connections to the LDAP directory during
      *                       authentication attempts and authorization queries
      */
     @SuppressWarnings({"UnusedDeclaration"})
     public void setContextFactory(LdapContextFactory contextFactory) {
         this.contextFactory = contextFactory;
     }
 
     /**
      * Returns the LdapContextFactory instance used to acquire connections to the LDAP directory during authentication
      * attempts and authorization queries.  Unless specified otherwise, the default is a {@link JndiLdapContextFactory}
      * instance.
      *
      * @return the LdapContextFactory instance used to acquire connections to the LDAP directory during
      *         authentication attempts and authorization queries
      */
     public LdapContextFactory getContextFactory() {
         return this.contextFactory;
     }
 
     /*--------------------------------------------
     |               M E T H O D S                |
     ============================================*/
 
     /**
      * Delegates to {@link #queryForAuthenticationInfo(org.apache.shiro.authc.AuthenticationToken, LdapContextFactory)},
      * wrapping any {@link NamingException}s in a Shiro {@link AuthenticationException} to satisfy the parent method
      * signature.
      *
      * @param token the authentication token containing the user's principal and credentials.
      * @return the {@link AuthenticationInfo} acquired after a successful authentication attempt
      * @throws AuthenticationException if the authentication attempt fails or if a
      *                                 {@link NamingException} occurs.
      */
     protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {
         AuthenticationInfo info;
         try {
             info = queryForAuthenticationInfo(token, getContextFactory());
         } catch (AuthenticationNotSupportedException e) {
             String msg = "Unsupported configured authentication mechanism";
             throw new UnsupportedAuthenticationMechanismException(msg, e);
         } catch (javax.naming.AuthenticationException e) {
             throw new AuthenticationException("LDAP authentication failed.", e);
         } catch (NamingException e) {
             String msg = "LDAP naming error while attempting to authenticate user.";
             throw new AuthenticationException(msg, e);
         }
 
         return info;
     }
 
 
     protected AuthorizationInfo doGetAuthorizationInfo(PrincipalCollection principals) {
         AuthorizationInfo info;
         try {
             info = queryForAuthorizationInfo(principals, getContextFactory());
         } catch (NamingException e) {
             String msg = "LDAP naming error while attempting to retrieve authorization for user [" + principals + "].";
             throw new AuthorizationException(msg, e);
         }
 
         return info;
     }
 
     /**
      * Returns the principal to use when creating the LDAP connection for an authentication attempt.
      * <p/>
      * This implementation uses a heuristic: it checks to see if the specified token's
      * {@link AuthenticationToken#getPrincipal() principal} is a {@code String}, and if so,
      * {@link #getUserDn(String) converts it} from what is
      * assumed to be a raw uid or username {@code String} into a User DN {@code String}.  Almost all LDAP directories
      * expect the authentication connection to present a User DN and not an unqualified username or uid.
      * <p/>
      * If the token's {@code principal} is not a String, it is assumed to already be in the format supported by the
      * underlying {@link LdapContextFactory} implementation and the raw principal is returned directly.
      *
      * @param token the {@link AuthenticationToken} submitted during the authentication process
      * @return the User DN or raw principal to use to acquire the LdapContext.
      * @see LdapContextFactory#getLdapContext(Object, Object)
      */
     protected Object getLdapPrincipal(AuthenticationToken token) {
         Object principal = token.getPrincipal();
         if (principal instanceof String) {
             String sPrincipal = (String) principal;
             return getUserDn(sPrincipal);
         }
         return principal;
     }
 
     /**
      * This implementation opens an LDAP connection using the token's
      * {@link #getLdapPrincipal(org.apache.shiro.authc.AuthenticationToken) discovered principal} and provided
      * {@link AuthenticationToken#getCredentials() credentials}.  If the connection opens successfully, the
      * authentication attempt is immediately considered successful and a new
      * {@link AuthenticationInfo} instance is
      * {@link #createAuthenticationInfo(org.apache.shiro.authc.AuthenticationToken, Object, Object, javax.naming.ldap.LdapContext) created}
      * and returned.  If the connection cannot be opened, either because LDAP authentication failed or some other
      * JNDI problem, an {@link NamingException} will be thrown.
      *
      * @param token              the submitted authentication token that triggered the authentication attempt.
      * @param ldapContextFactory factory used to retrieve LDAP connections.
      * @return an {@link AuthenticationInfo} instance representing the authenticated user's information.
      * @throws NamingException if any LDAP errors occur.
      */
     protected AuthenticationInfo queryForAuthenticationInfo(AuthenticationToken token,
                                                             LdapContextFactory ldapContextFactory)
             throws NamingException {
 
         Object principal = token.getPrincipal();
         Object credentials = token.getCredentials();
 
         log.debug("Authenticating user '{}' through LDAP", principal);
 
         principal = getLdapPrincipal(token);
 
         LdapContext ctx = null;
         try {
             ctx = ldapContextFactory.getLdapContext(principal, credentials);
             //context was opened successfully, which means their credentials were valid.  Return the AuthenticationInfo:
             return createAuthenticationInfo(token, principal, credentials, ctx);
         } finally {
             LdapUtils.closeContext(ctx);
         }
     }
 
     /**
      * Returns the {@link AuthenticationInfo} resulting from a Subject's successful LDAP authentication attempt.
      * <p/>
      * This implementation ignores the {@code ldapPrincipal}, {@code ldapCredentials}, and the opened
      * {@code ldapContext} arguments and merely returns an {@code AuthenticationInfo} instance mirroring the
      * submitted token's principal and credentials.  This is acceptable because this method is only ever invoked after
      * a successful authentication attempt, which means the provided principal and credentials were correct, and can
      * be used directly to populate the (now verified) {@code AuthenticationInfo}.
      * <p/>
      * Subclasses however are free to override this method for more advanced construction logic.
      *
      * @param token           the submitted {@code AuthenticationToken} that resulted in a successful authentication
      * @param ldapPrincipal   the LDAP principal used when creating the LDAP connection.  Unlike the token's
      *                        {@link AuthenticationToken#getPrincipal() principal}, this value is usually a constructed
      *                        User DN and not a simple username or uid.  The exact value is depending on the
      *                        configured
      *                        <a href="http://download-llnw.oracle.com/javase/tutorial/jndi/ldap/auth_mechs.html">
      *                        LDAP authentication mechanism</a> in use.
      * @param ldapCredentials the LDAP credentials used when creating the LDAP connection.
      * @param ldapContext     the LdapContext created that resulted in a successful authentication.  It can be used
      *                        further by subclasses for more complex operations.  It does not need to be closed -
      *                        it will be closed automatically after this method returns.
      * @return the {@link AuthenticationInfo} resulting from a Subject's successful LDAP authentication attempt.
      * @throws NamingException if there was any problem using the {@code LdapContext}
      */
     @SuppressWarnings({"UnusedDeclaration"})
     protected AuthenticationInfo createAuthenticationInfo(AuthenticationToken token, Object ldapPrincipal,
                                                           Object ldapCredentials, LdapContext ldapContext)
             throws NamingException {
         return new SimpleAuthenticationInfo(token.getPrincipal(), token.getCredentials(), getName());
     }
 
 
     /**
      * Method that should be implemented by subclasses to build an
      * {@link AuthorizationInfo} object by querying the LDAP context for the
      * specified principal.</p>
      *
      * @param principals          the principals of the Subject whose AuthenticationInfo should be queried from the LDAP server.
      * @param ldapContextFactory factory used to retrieve LDAP connections.
      * @return an {@link AuthorizationInfo} instance containing information retrieved from the LDAP server.
      * @throws NamingException if any LDAP errors occur during the search.
      */
     protected AuthorizationInfo queryForAuthorizationInfo(PrincipalCollection principals,
                                                           LdapContextFactory ldapContextFactory) throws NamingException {
         return null;
     }
 }