/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License, Version 1.0 only
 * (the "License").  You may not use this file except in compliance
 * with the License.
 *
 * You can obtain a copy of the license at
 * docs/licenses/cddl.txt
 * or http://www.opensource.org/licenses/cddl1.php.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at
 * docs/licenses/cddl.txt.  If applicable,
 * add the following below this CDDL HEADER, with the fields enclosed
 * by brackets "[]" replaced with your own identifying information:
 *      Portions Copyright [yyyy] [name of copyright owner]
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 * CDDL HEADER END
 *
 *
 *      Copyright 2010-2021 Ping Identity Corporation
 */
package com.unboundid.directory.sdk.http.api;


import com.unboundid.directory.sdk.http.config.OAuthTokenHandlerConfig;
import com.unboundid.directory.sdk.common.internal.ExampleUsageProvider;
import com.unboundid.directory.sdk.common.internal.Reconfigurable;
import com.unboundid.directory.sdk.common.internal.UnboundIDExtension;
import com.unboundid.directory.sdk.ds.internal.DirectoryServerExtension;
import com.unboundid.directory.sdk.http.types.HTTPServerContext;
import com.unboundid.directory.sdk.proxy.internal.DirectoryProxyServerExtension;
import com.unboundid.ldap.sdk.DN;
import com.unboundid.ldap.sdk.LDAPException;
import com.unboundid.ldap.sdk.ResultCode;
import com.unboundid.scim.sdk.OAuthToken;
import com.unboundid.scim.sdk.SCIMRequest;
import com.unboundid.scim.sdk.OAuthTokenStatus;
import com.unboundid.util.Extensible;
import com.unboundid.util.ThreadSafety;
import com.unboundid.util.ThreadSafetyLevel;
import com.unboundid.util.args.ArgumentException;
import com.unboundid.util.args.ArgumentParser;

import java.security.GeneralSecurityException;
import java.util.Collections;
import java.util.List;
import java.util.Map;


/**
 * This class defines an API that must be implemented by extensions which will
 * handle incoming SCIM requests with OAuth 2.0 bearer token authentication.
 * The OAuthTokenHandler is responsible for decoding the bearer token and
 * checking it for authenticity and validity.
 * <BR><BR>
 * OAuth provides a method for clients to access a protected resource on
 * behalf of a resource owner. In the general case, before a client can
 * access a protected resource, it must first obtain an authorization
 * grant from the resource owner and then exchange the authorization
 * grant for an access token. The access token represents the grant's
 * scope, duration, and other attributes specified by the authorization
 * grant. The client accesses the protected resource by presenting the
 * access token to the resource server (i.e. the Directory or Proxy Server with
 * the SCIM HTTP Servlet enabled).
 * <BR><BR>
 * The access token provides an abstraction, replacing different
 * authorization constructs (e.g., username and password, assertion) for
 * a single token understood by the resource server. This abstraction
 * enables issuing access tokens valid for a short time period, as well
 * as removing the resource server's need to understand a wide range of
 * authentication schemes. See "OAuth 2.0 Authorization Framework: Bearer
 * Token Usage" (<i>RFC 6750</i>) for the full
 * specification and details.
 * <BR><BR>
 * TLS security is required to use OAuth 2.0 bearer tokens, as specified in
 * <i>RFC 6750</i>. A bearer token may be used by any party
 * in possession of that token (the "bearer"), and thus needs to be protected
 * when transmitted across the network. Implementations of this API should take
 * special care to verify that the token came from a trusted source (using a
 * secret key or some other signing mechanism to prove that the token is
 * authentic). Please read "OAuth 2.0 Threat Model and Security Considerations"
 * (<i>RFC 6819</i>) for a comprehensive list of
 * security threats to consider when working with OAuth bearer tokens.
 * <BR><BR>
 * The OAuthTokenHandler is also responsible for extracting an authorization DN
 * from the bearer token (or otherwise providing one), which will be used to
 * apply access controls before returning the protected resource. There are also
 * methods to extract the expiration date of the token as well as verify that
 * the intended audience is this server (to deal with token redirect).
 * <BR><BR>
 * The order these methods are called by the SCIM HTTP Servlet Extension is as
 * follows:
 * <ol>
 *   <li><i>decodeOAuthToken()</i></li>
 *   <li><i>isTokenAuthentic()</i></li>
 *   <li><i>isTokenForThisServer()</i></li>
 *   <li><i>isTokenExpired()</i></li>
 *   <li><i>validateToken()</i></li>
 *   <li><i>getAuthzDN()</i></li>
 * </ol>
 * If any of the methods fail or return an error result, the server will return
 * an appropriate "unauthorized" response to the client.
 * <BR>
 * <H2>Configuring OAuth Token Handlers</H2>
 * In order to configure a token handler created using this API, use a command
 * like:
 * <PRE>
 *      dsconfig create-oauth-token-handler \
 *           --handler-name "<I>{handler-name}</I>" \
 *           --type third-party \
 *           --set "extension-class:<I>{class-name}</I>" \
 *           --set "extension-argument:<I>{name=value}</I>"
 * </PRE>
 * where "<I>{handler-name}</I>" is the name to use for the token handler
 * instance, "<I>{class-name}</I>" is the fully-qualified name of the Java class
 * that extends {@code com.unboundid.directory.sdk.http.api.OAuthTokenHandler},
 * and "<I>{name=value}</I>" represents name-value pairs for any arguments to
 * provide to the token handler.  If multiple arguments should be provided to
 * the token handler, then the
 * "<CODE>--set extension-argument:<I>{name=value}</I></CODE>" option should be
 * provided multiple times.
 *
 * @see  com.unboundid.directory.sdk.http.scripting.ScriptedOAuthTokenHandler
 */
@Extensible()
@DirectoryServerExtension()
@DirectoryProxyServerExtension(appliesToLocalContent=false,
     appliesToRemoteContent=true)
@ThreadSafety(level=ThreadSafetyLevel.INTERFACE_THREADSAFE)
public abstract class OAuthTokenHandler
       implements UnboundIDExtension, Reconfigurable<OAuthTokenHandlerConfig>,
                  ExampleUsageProvider
{
  /**
   * Creates a new instance of this token handler.  All token handler
   * implementations must include a default constructor, but any initialization
   * should generally be done in the {@code initializeTokenHandler} method.
   */
  public OAuthTokenHandler()
  {
    // No implementation is required.
  }



  /**
   * {@inheritDoc}
   */
  @Override
  public abstract String getExtensionName();



  /**
   * {@inheritDoc}
   */
  @Override
  public abstract String[] getExtensionDescription();



  /**
   * {@inheritDoc}
   */
  @Override
  public void defineConfigArguments(final ArgumentParser parser)
         throws ArgumentException
  {
    // No arguments will be allowed by default.
  }



  /**
   * Initializes this token handler.
   *
   * @param  serverContext  A handle to the server context for the server in
   *                        which this extension is running.
   * @param  config         The general configuration for this token handler.
   * @param  parser         The argument parser which has been initialized from
   *                        the configuration for this token handler.
   *
   * @throws  LDAPException  If a problem occurs while initializing this token
   *                         handler.
   */
  public void initializeTokenHandler(final HTTPServerContext serverContext,
                                     final OAuthTokenHandlerConfig config,
                                     final ArgumentParser parser)
         throws LDAPException
  {
    // No initialization will be performed by default.
  }



  /**
   * {@inheritDoc}
   */
  @Override
  public boolean isConfigurationAcceptable(final OAuthTokenHandlerConfig config,
                      final ArgumentParser parser,
                      final List<String> unacceptableReasons)
  {
    // No extended validation will be performed by default.
    return true;
  }



  /**
   * {@inheritDoc}
   */
  @Override
  public ResultCode applyConfiguration(final OAuthTokenHandlerConfig config,
                                       final ArgumentParser parser,
                                       final List<String> adminActionsRequired,
                                       final List<String> messages)
  {
    // By default, no configuration changes will be applied.  If there are any
    // arguments, then add an admin action message indicating that the extension
    // needs to be restarted for any changes to take effect.
    if (! parser.getNamedArguments().isEmpty())
    {
      adminActionsRequired.add(
        "No configuration change has actually been applied. The new " +
        "configuration will not take effect until the HTTP Connection " +
        "Handler is disabled and re-enabled or until the server is restarted.");
    }

    return ResultCode.SUCCESS;
  }



  /**
   * Performs any cleanup which may be necessary when this token handler is to
   * be taken out of service.
   */
  public void finalizeTokenHandler()
  {
    // No implementation is required.
  }



  /**
   * {@inheritDoc}
   */
  @Override
  public Map<List<String>,String> getExamplesArgumentSets()
  {
    return Collections.emptyMap();
  }



  /**
   * Creates an {@link OAuthToken} instance from the incoming token value.
   * <p>
   * Implementers may choose to return a subclass of {@link OAuthToken} in order
   * to provide convenience methods for interacting with the token. This can be
   * helpful because the returned {@link OAuthToken} is passed to all of the
   * other methods in this class.
   *
   * @param base64TokenValue the base64-encoded bearer token value
   * @return a {@link OAuthToken} instance. This must not be {@code null}.
   * @throws GeneralSecurityException if there is an error decoding the token
   */
  public abstract OAuthToken decodeOAuthToken(final String base64TokenValue)
          throws GeneralSecurityException;



  /**
   * Determines whether the given token is expired.
   *
   * @param token the OAuth 2.0 bearer token.
   * @return {@code true} if the token is already expired, {@code false} if not.
   * @throws GeneralSecurityException if there is an error determining the
   *         token's expiration date
   */
  public abstract boolean isTokenExpired(final OAuthToken token)
          throws GeneralSecurityException;



  /**
   * Determines whether the incoming token is authentic (i.e. that it came from
   * a trusted authorization server and not an attacker). Implementers are
   * encouraged to use signed tokens and use this method to verify the
   * signature, but other methods such as symmetric key encryption (using a
   * shared secret) can be used as well.
   *
   * @param token the OAuth 2.0 bearer token.
   * @return {@code true} if the bearer token can be verified as authentic and
   *         originating from a trusted source, {@code false} if not.
   * @throws GeneralSecurityException if there is an error determining whether
   *         the token is authentic
   */
  public abstract boolean isTokenAuthentic(final OAuthToken token)
          throws GeneralSecurityException;



  /**
   * Determines whether the incoming token is targeted for this server. This
   * allows the implementation to reject the token early in the validation
   * process if it can see that the intended recipient was not this server.
   *
   * @param token the OAuth 2.0 bearer token.
   * @return {@code true} if the bearer token identifies this server as the
   *         intended recipient, {@code false} if not.
   * @throws GeneralSecurityException if there is an error determining whether
   *         the token is for this server
   */
  public abstract boolean isTokenForThisServer(final OAuthToken token)
          throws GeneralSecurityException;



  /**
   * Determines whether the incoming token is valid for the given request. This
   * method should verify that the token is legitimate and grants access to the
   * requested resource specified in the {@link SCIMRequest}. This typically
   * involves checking the token scope and any other attributes granted by the
   * authorization grant. Implementations may need to call back to the
   * authorization server to verify that the token is still valid and has not
   * been revoked.
   *
   * @param token the OAuth 2.0 bearer token.
   * @param scimRequest the {@link SCIMRequest} that we are validating.
   * @return an {@link OAuthTokenStatus} object which indicates whether the
   *         bearer token is valid and grants access to the target resource.
   *         This must not be {@code null}.
   * @throws GeneralSecurityException if there is an error determining whether
   *         the token is valid
   */
  public abstract OAuthTokenStatus validateToken(final OAuthToken token,
                                                 final SCIMRequest scimRequest)
          throws GeneralSecurityException;



  /**
   * Extracts the DN of the authorization entry (for which to apply access
   * controls) from the incoming token.
   * <p>
   * This may require performing an LDAP search in order to find the DN that
   * matches a certain attribute value contained in the token.
   *
   * @param token the OAuth 2.0 bearer token.
   * @return the authorization DN to use.
   * @throws GeneralSecurityException if there is an error determining the
   *         authorization user DN
   */
  public abstract DN getAuthzDN(final OAuthToken token)
          throws GeneralSecurityException;
}