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Java library for Javascript Object Signing and Encryption (JOSE) and JSON Web Tokens (JWT)
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/*
 * nimbus-jose-jwt
 *
 * Copyright 2012-2016, Connect2id Ltd and contributors.
 *
 * Licensed 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 com.nimbusds.jose.crypto.impl;


import java.util.Collections;
import java.util.Set;

import com.nimbusds.jose.*;


/**
 * Critical ({@code crit}) header parameters deferral policy.
 *
 * @see CriticalHeaderParamsAware
 *
 * @author Vladimir Dzhuvinov
 * @version 2020-04-17
 */
public class CriticalHeaderParamsDeferral {


	/**
	 * The names of the deferred critical headers.
	 */
	private Set deferredParams = Collections.emptySet();


	/**
	 * Returns the names of the critical ({@code crit}) header parameters
	 * that are understood and processed.
	 *
	 * @return Empty immutable set.
	 */
	public Set getProcessedCriticalHeaderParams() {

		return Collections.singleton(HeaderParameterNames.BASE64_URL_ENCODE_PAYLOAD);
	}


	/**
	 * Returns the names of the critical ({@code crit}) header parameters
	 * that are deferred to the application for processing.
	 *
	 * @return The names of the critical header parameters that are
	 *         deferred to the application for processing, as an
	 *         unmodifiable set, empty set if none.
	 */
	public Set getDeferredCriticalHeaderParams() {

		return Collections.unmodifiableSet(deferredParams);
	}


	/**
	 * Sets the names of the critical ({@code crit}) header parameters
	 * that are deferred to the application for processing.
	 *
	 * @param defCritHeaders The names of the critical header parameters
	 *                       that are deferred to the application for
	 *                       processing, empty set or {@code null} if none.
	 */
	public void setDeferredCriticalHeaderParams(final Set defCritHeaders) {

		if (defCritHeaders == null) {
			this.deferredParams = Collections.emptySet();
		} else {
			this.deferredParams = defCritHeaders;
		}
	}


	/**
	 * Returns {@code true} if the specified header passes the critical
	 * parameters check.
	 *
	 * @param header The JWS or JWE header to check. Must not be
	 *               {@code null}.
	 *
	 * @return {@code true} if the header passes, {@code false} if the
	 *         header contains one or more critical header parameters which
	 *         are not marked for deferral to the application.
	 */
	public boolean headerPasses(final Header header) {

		if (header.getCriticalParams() == null) {
			return true; // ok
		}
		
		for (String critParam: header.getCriticalParams()) {
			if (getProcessedCriticalHeaderParams().contains(critParam)) {
				continue;
			}
			if (getDeferredCriticalHeaderParams().contains(critParam)) {
				continue;
			}
			return false;
		}
		return true;
	}


	/**
	 * Throws a JOSE exception if the specified JWE header doesn't pass the
	 * critical header parameters check.
	 *
	 * @param header The JWE header to check. Must not be {@code null}.
	 *
	 * @throws JOSEException If the JWE header doesn't pass the check.
	 */
	public void ensureHeaderPasses(final JWEHeader header)
		throws JOSEException {

		if (! headerPasses(header)) {
			throw new JOSEException("Unsupported critical header parameter(s)");
		}
	}
}