Add support for custom grant types

Closes gh-14657

oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/endpoint/RestClientOAuth2AccessTokenResponseClient.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2002-2024 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.oauth2.client.endpoint;
+
+import org.springframework.security.oauth2.core.endpoint.OAuth2AccessTokenResponse;
+
+/**
+ * An implementation of {@link OAuth2AccessTokenResponseClient} that "exchanges"
+ * user-defined credentials for an access token at the Authorization Server's Token
+ * Endpoint.
+ *
+ * @author Steve Riesenberg
+ * @since 6.4
+ * @see OAuth2AccessTokenResponseClient
+ * @see OAuth2AccessTokenResponse
+ */
+public final class RestClientOAuth2AccessTokenResponseClient<T extends AbstractOAuth2AuthorizationGrantRequest>
+		extends AbstractRestClientOAuth2AccessTokenResponseClient<T> {
+
+}

oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/endpoint/WebClientReactiveOAuth2AccessTokenResponseClient.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2002-2024 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.oauth2.client.endpoint;
+
+import org.springframework.security.oauth2.core.endpoint.OAuth2AccessTokenResponse;
+
+/**
+ * An implementation of {@link ReactiveOAuth2AccessTokenResponseClient} that
+ * "exchanges" user-defined credentials for an access token at the Authorization
+ * Server's Token Endpoint.
+ *
+ * @author Steve Riesenberg
+ * @since 6.4
+ * @see OAuth2AccessTokenResponseClient
+ * @see OAuth2AccessTokenResponse
+ */
+public final class WebClientReactiveOAuth2AccessTokenResponseClient<T extends AbstractOAuth2AuthorizationGrantRequest>
+		extends AbstractWebClientReactiveOAuth2AccessTokenResponseClient<T> {
+
+}