Don't force downcasting of RequestAttributes to ServletRequestAttributes

Fixes gh-7952

config/src/test/java/org/springframework/security/config/annotation/web/configuration/SecurityReactorContextConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * 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.
@@ -28,6 +28,7 @@ import org.springframework.security.config.test.SpringTestRule;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.security.oauth2.client.web.reactive.function.client.MockExchangeFunction;
+import org.springframework.web.context.request.RequestAttributes;
 import org.springframework.web.context.request.RequestContextHolder;
 import org.springframework.web.context.request.ServletRequestAttributes;
 import org.springframework.web.reactive.function.client.ClientRequest;
@@ -36,6 +37,7 @@ import org.springframework.web.reactive.function.client.ExchangeFilterFunction;
 import reactor.core.CoreSubscriber;
 import reactor.core.publisher.BaseSubscriber;
 import reactor.core.publisher.Mono;
+import reactor.core.publisher.Operators;
 import reactor.test.StepVerifier;
 import reactor.util.context.Context;
 
@@ -139,6 +141,52 @@ public class SecurityReactorContextConfigurationTests {
 		assertThat(resultContext).isSameAs(parentContext);
 	}
 
+	@Test
+	public void createSubscriberIfNecessaryWhenNotServletRequestAttributesThenStillCreate() {
+		RequestContextHolder.setRequestAttributes(
+				new RequestAttributes() {
+					@Override
+					public Object getAttribute(String name, int scope) {
+						return null;
+					}
+
+					@Override
+					public void setAttribute(String name, Object value, int scope) {
+					}
+
+					@Override
+					public void removeAttribute(String name, int scope) {
+					}
+
+					@Override
+					public String[] getAttributeNames(int scope) {
+						return new String[0];
+					}
+
+					@Override
+					public void registerDestructionCallback(String name, Runnable callback, int scope) {
+					}
+
+					@Override
+					public Object resolveReference(String key) {
+						return null;
+					}
+
+					@Override
+					public String getSessionId() {
+						return null;
+					}
+
+					@Override
+					public Object getSessionMutex() {
+						return null;
+					}
+				});
+
+		CoreSubscriber<Object> subscriber = this.subscriberRegistrar.createSubscriberIfNecessary(Operators.emptySubscriber());
+		assertThat(subscriber).isInstanceOf(SecurityReactorContextConfiguration.SecurityReactorContextSubscriber.class);
+	}
+
 	@Test
 	public void createPublisherWhenLastOperatorAddedThenSecurityContextAttributesAvailable() {
 		// Trigger the importing of SecurityReactorContextConfiguration via OAuth2ImportSelector