Add reactive support for BREACH

Closes gh-11959

web/src/main/java/org/springframework/security/web/server/csrf/XorServerCsrfTokenRequestAttributeHandler.java

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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.springframework.security.web.server.csrf;
+
+import java.security.SecureRandom;
+import java.util.Base64;
+
+import reactor.core.publisher.Mono;
+
+import org.springframework.security.crypto.codec.Utf8;
+import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebExchange;
+
+/**
+ * An implementation of the {@link ServerCsrfTokenRequestAttributeHandler} and
+ * {@link ServerCsrfTokenRequestResolver} interfaces that is capable of masking the value
+ * of the {@link CsrfToken} on each request and resolving the raw token value from the
+ * masked value as either a form data value or header of the request.
+ *
+ * @author Steve Riesenberg
+ * @since 5.8
+ */
+public final class XorServerCsrfTokenRequestAttributeHandler extends ServerCsrfTokenRequestAttributeHandler {
+
+	private SecureRandom secureRandom = new SecureRandom();
+
+	/**
+	 * Specifies the {@code SecureRandom} used to generate random bytes that are used to
+	 * mask the value of the {@link CsrfToken} on each request.
+	 * @param secureRandom the {@code SecureRandom} to use to generate random bytes
+	 */
+	public void setSecureRandom(SecureRandom secureRandom) {
+		Assert.notNull(secureRandom, "secureRandom cannot be null");
+		this.secureRandom = secureRandom;
+	}
+
+	@Override
+	public void handle(ServerWebExchange exchange, Mono<CsrfToken> csrfToken) {
+		Assert.notNull(exchange, "exchange cannot be null");
+		Assert.notNull(csrfToken, "csrfToken cannot be null");
+		Mono<CsrfToken> updatedCsrfToken = csrfToken.map((token) -> new DefaultCsrfToken(token.getHeaderName(),
+				token.getParameterName(), createXoredCsrfToken(this.secureRandom, token.getToken())));
+		super.handle(exchange, updatedCsrfToken);
+	}
+
+	@Override
+	public Mono<String> resolveCsrfTokenValue(ServerWebExchange exchange, CsrfToken csrfToken) {
+		return super.resolveCsrfTokenValue(exchange, csrfToken)
+				.flatMap((actualToken) -> Mono.justOrEmpty(getTokenValue(actualToken, csrfToken.getToken())));
+	}
+
+	private static String getTokenValue(String actualToken, String token) {
+		byte[] actualBytes;
+		try {
+			actualBytes = Base64.getUrlDecoder().decode(actualToken);
+		}
+		catch (Exception ex) {
+			return null;
+		}
+
+		byte[] tokenBytes = Utf8.encode(token);
+		int tokenSize = tokenBytes.length;
+		if (actualBytes.length < tokenSize) {
+			return null;
+		}
+
+		// extract token and random bytes
+		int randomBytesSize = actualBytes.length - tokenSize;
+		byte[] xoredCsrf = new byte[tokenSize];
+		byte[] randomBytes = new byte[randomBytesSize];
+
+		System.arraycopy(actualBytes, 0, randomBytes, 0, randomBytesSize);
+		System.arraycopy(actualBytes, randomBytesSize, xoredCsrf, 0, tokenSize);
+
+		byte[] csrfBytes = xorCsrf(randomBytes, xoredCsrf);
+		return Utf8.decode(csrfBytes);
+	}
+
+	private static String createXoredCsrfToken(SecureRandom secureRandom, String token) {
+		byte[] tokenBytes = Utf8.encode(token);
+		byte[] randomBytes = new byte[tokenBytes.length];
+		secureRandom.nextBytes(randomBytes);
+
+		byte[] xoredBytes = xorCsrf(randomBytes, tokenBytes);
+		byte[] combinedBytes = new byte[tokenBytes.length + randomBytes.length];
+		System.arraycopy(randomBytes, 0, combinedBytes, 0, randomBytes.length);
+		System.arraycopy(xoredBytes, 0, combinedBytes, randomBytes.length, xoredBytes.length);
+
+		return Base64.getUrlEncoder().encodeToString(combinedBytes);
+	}
+
+	private static byte[] xorCsrf(byte[] randomBytes, byte[] csrfBytes) {
+		int len = Math.min(randomBytes.length, csrfBytes.length);
+		byte[] xoredCsrf = new byte[len];
+		System.arraycopy(csrfBytes, 0, xoredCsrf, 0, csrfBytes.length);
+		for (int i = 0; i < len; i++) {
+			xoredCsrf[i] ^= randomBytes[i];
+		}
+		return xoredCsrf;
+	}
+
+}