SigningKeyResolverAdapter.java

/*
 * Copyright (C) 2014 jsonwebtoken.io
 *
 * 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 io.jsonwebtoken;

import io.jsonwebtoken.lang.Assert;

import javax.crypto.spec.SecretKeySpec;
import java.security.Key;

/**
 * An <a href="http://en.wikipedia.org/wiki/Adapter_pattern">Adapter</a> implementation of the
 * {@link SigningKeyResolver} interface that allows subclasses to process only the type of JWS body that
 * is known/expected for a particular case.
 *
 * <p>The {@link #resolveSigningKey(JwsHeader, Claims)} and {@link #resolveSigningKey(JwsHeader, String)} method
 * implementations delegate to the
 * {@link #resolveSigningKeyBytes(JwsHeader, Claims)} and {@link #resolveSigningKeyBytes(JwsHeader, String)} methods
 * respectively.  The latter two methods simply throw exceptions:  they represent scenarios expected by
 * calling code in known situations, and it is expected that you override the implementation in those known situations;
 * non-overridden *KeyBytes methods indicates that the JWS input was unexpected.</p>
 *
 * <p>If either {@link #resolveSigningKey(JwsHeader, String)} or {@link #resolveSigningKey(JwsHeader, Claims)}
 * are not overridden, one (or both) of the *KeyBytes variants must be overridden depending on your expected
 * use case.  You do not have to override any method that does not represent an expected condition.</p>
 *
 * @since 0.4
 */
public class SigningKeyResolverAdapter implements SigningKeyResolver {

    @Override
    public Key resolveSigningKey(JwsHeader header, Claims claims) {
        SignatureAlgorithm alg = SignatureAlgorithm.forName(header.getAlgorithm());
        Assert.isTrue(alg.isHmac(), "The default resolveSigningKey(JwsHeader, Claims) implementation cannot be " +
                                    "used for asymmetric key algorithms (RSA, Elliptic Curve).  " +
                                    "Override the resolveSigningKey(JwsHeader, Claims) method instead and return a " +
                                    "Key instance appropriate for the " + alg.name() + " algorithm.");
        byte[] keyBytes = resolveSigningKeyBytes(header, claims);
        return new SecretKeySpec(keyBytes, alg.getJcaName());
    }

    @Override
    public Key resolveSigningKey(JwsHeader header, String plaintext) {
        SignatureAlgorithm alg = SignatureAlgorithm.forName(header.getAlgorithm());
        Assert.isTrue(alg.isHmac(), "The default resolveSigningKey(JwsHeader, String) implementation cannot be " +
                                    "used for asymmetric key algorithms (RSA, Elliptic Curve).  " +
                                    "Override the resolveSigningKey(JwsHeader, String) method instead and return a " +
                                    "Key instance appropriate for the " + alg.name() + " algorithm.");
        byte[] keyBytes = resolveSigningKeyBytes(header, plaintext);
        return new SecretKeySpec(keyBytes, alg.getJcaName());
    }

    /**
     * Convenience method invoked by {@link #resolveSigningKey(JwsHeader, Claims)} that obtains the necessary signing
     * key bytes.  This implementation simply throws an exception: if the JWS parsed is a Claims JWS, you must
     * override this method or the {@link #resolveSigningKey(JwsHeader, Claims)} method instead.
     *
     * <p><b>NOTE:</b> You cannot override this method when validating RSA signatures.  If you expect RSA signatures,
     * you must override the {@link #resolveSigningKey(JwsHeader, Claims)} method instead.</p>
     *
     * @param header the parsed {@link JwsHeader}
     * @param claims the parsed {@link Claims}
     * @return the signing key bytes to use to verify the JWS signature.
     */
    public byte[] resolveSigningKeyBytes(JwsHeader header, Claims claims) {
        throw new UnsupportedJwtException("The specified SigningKeyResolver implementation does not support " +
                                          "Claims JWS signing key resolution.  Consider overriding either the " +
                                          "resolveSigningKey(JwsHeader, Claims) method or, for HMAC algorithms, the " +
                                          "resolveSigningKeyBytes(JwsHeader, Claims) method.");
    }

    /**
     * Convenience method invoked by {@link #resolveSigningKey(JwsHeader, String)} that obtains the necessary signing
     * key bytes.  This implementation simply throws an exception: if the JWS parsed is a plaintext JWS, you must
     * override this method or the {@link #resolveSigningKey(JwsHeader, String)} method instead.
     *
     * @param header the parsed {@link JwsHeader}
     * @param payload the parsed String plaintext payload
     * @return the signing key bytes to use to verify the JWS signature.
     */
    public byte[] resolveSigningKeyBytes(JwsHeader header, String payload) {
        throw new UnsupportedJwtException("The specified SigningKeyResolver implementation does not support " +
                                          "plaintext JWS signing key resolution.  Consider overriding either the " +
                                          "resolveSigningKey(JwsHeader, String) method or, for HMAC algorithms, the " +
                                          "resolveSigningKeyBytes(JwsHeader, String) method.");
    }
}