Introduce AuthenticationConverterServerWebExchangeMatcher

AuthenticationConverterServerWebExchangeMatcher is ServerWebExchangeMatcher implementation based on AuthenticationConverter which matches if ServerWebExchange can be converted to Authentication.
It can be used as a matcher where SecurityFilterChain should be matched based on used authentication method.
BearerTokenServerWebExchangeMatcher was replaced by this matcher.

Closes gh-8824

web/src/main/java/org/springframework/security/web/server/authentication/AuthenticationConverterServerWebExchangeMatcher.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2002-2020 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.authentication;
+
+import static org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcher.MatchResult.match;
+import static org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcher.MatchResult.notMatch;
+
+import org.springframework.security.core.Authentication;
+import org.springframework.security.web.server.util.matcher.ServerWebExchangeMatcher;
+import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebExchange;
+
+import reactor.core.publisher.Mono;
+
+/**
+ * Matches if the {@link ServerAuthenticationConverter} can convert a {@link ServerWebExchange} to an {@link Authentication}.
+ *
+ * @author David Kovac
+ * @since 5.4
+ * @see ServerAuthenticationConverter
+ */
+public final class AuthenticationConverterServerWebExchangeMatcher implements ServerWebExchangeMatcher {
+	private final ServerAuthenticationConverter serverAuthenticationConverter;
+
+	public AuthenticationConverterServerWebExchangeMatcher(ServerAuthenticationConverter serverAuthenticationConverter) {
+		Assert.notNull(serverAuthenticationConverter, "serverAuthenticationConverter cannot be null");
+		this.serverAuthenticationConverter = serverAuthenticationConverter;
+	}
+
+	@Override
+	public Mono<MatchResult> matches(ServerWebExchange exchange) {
+		return this.serverAuthenticationConverter.convert(exchange)
+				.flatMap(a -> match())
+				.onErrorResume(e -> notMatch())
+				.switchIfEmpty(notMatch());
+	}
+}