Resolve oauth2 client placeholders

Closes gh-8453

config/src/test/resources/org/springframework/security/config/oauth2/client/ClientRegistrationsBeanDefinitionParserTests-ClientPlaceholders.xml

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  ~ 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.
+  -->
+
+<b:beans xmlns:b="http://www.springframework.org/schema/beans"
+		 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xmlns="http://www.springframework.org/schema/security"
+		 xsi:schemaLocation="
+			http://www.springframework.org/schema/security
+			https://www.springframework.org/schema/security/spring-security.xsd
+			http://www.springframework.org/schema/beans
+			https://www.springframework.org/schema/beans/spring-beans.xsd">
+	<client-registrations>
+		<client-registration registration-id="github"
+							 client-id="${oauth2.client.id}"
+							 client-secret="${oauth2.client.secret}"
+							 provider-id="github"/>
+	</client-registrations>
+</b:beans>