Introduce AuthenticationManagerResolver

Suitable for multi-tenant applications needing to branch
authentication strategies based on request details.

Fixes: gh-6722

Author: jzheaux

core/src/main/java/org/springframework/security/authentication/AuthenticationManagerResolver.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2002-2019 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.authentication;
+
+/**
+ * An interface for resolving an {@link AuthenticationManager} based on the provided context
+ *
+ * @author Josh Cummings
+ * @since 5.2
+ */
+public interface AuthenticationManagerResolver<C> {
+
+	/**
+	 * Resolve an {@link AuthenticationManager} from a provided context
+	 * @param context
+	 * @return the {@link AuthenticationManager} to use
+	 */
+	AuthenticationManager resolve(C context);
+}