Make single definition of defaultRolePrefix and rolePrefix

Previous to this commit, role prefix had to be set in every class
causing repetition. Now, bean `GrantedAuthorityDefaults` can be used to
define the role prefix in a single point.

Fixes gh-3701

core/src/main/java/org/springframework/security/config/GrantedAuthorityDefaults.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2002-2016 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
+ *
+ *      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 org.springframework.security.config;
+
+/**
+ * @author Eddú Meléndez
+ * @since 4.2.0
+ */
+public class GrantedAuthorityDefaults {
+
+	private String rolePrefix = "ROLE_";
+
+	public GrantedAuthorityDefaults(String rolePrefix) {
+		this.rolePrefix = rolePrefix;
+	}
+
+	public String getRolePrefix() {
+		return this.rolePrefix;
+	}
+
+	public void setRolePrefix(String rolePrefix) {
+		this.rolePrefix = rolePrefix;
+	}
+
+}