Change ResponseType from enum to class

Fixes gh-4292

oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/authentication/DefaultAuthorizationRequestUriBuilder.java

@@ -38,7 +38,7 @@ public class DefaultAuthorizationRequestUriBuilder implements AuthorizationReque
 	public URI build(AuthorizationRequestAttributes authorizationRequestAttributes) {
 		UriComponentsBuilder uriBuilder = UriComponentsBuilder
 				.fromUriString(authorizationRequestAttributes.getAuthorizeUri())
-				.queryParam(OAuth2Parameter.RESPONSE_TYPE, ResponseType.CODE.value());
+				.queryParam(OAuth2Parameter.RESPONSE_TYPE, ResponseType.CODE.getValue());
 		if (authorizationRequestAttributes.getRedirectUri() != null) {
 			uriBuilder.queryParam(OAuth2Parameter.REDIRECT_URI, authorizationRequestAttributes.getRedirectUri());
 		}

oauth2/oauth2-core/src/main/java/org/springframework/security/oauth2/core/endpoint/ResponseType.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.security.oauth2.core.endpoint;
 
+import org.springframework.util.Assert;
+
 /**
  * The <i>response_type</i> parameter is consumed by the authorization endpoint which
  * is used by the authorization code grant type and implicit grant type flows.
@@ -31,16 +33,33 @@ package org.springframework.security.oauth2.core.endpoint;
  * @since 5.0
  * @see <a target="_blank" href="https://tools.ietf.org/html/rfc6749#section-3.1.1">Section 3.1.1 Response Type</a>
  */
-public enum ResponseType {
-	CODE("code");
-
+public final class ResponseType {
+	public static final ResponseType CODE = new ResponseType("code");
 	private final String value;
 
-	ResponseType(String value) {
+	public ResponseType(String value) {
+		Assert.hasText(value, "value cannot be empty");
 		this.value = value;
 	}
 
-	public String value() {
+	public String getValue() {
 		return this.value;
 	}
+
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj) {
+			return true;
+		}
+		if (obj == null || this.getClass() != obj.getClass()) {
+			return false;
+		}
+		ResponseType that = (ResponseType) obj;
+		return this.getValue().equals(that.getValue());
+	}
+
+	@Override
+	public int hashCode() {
+		return this.getValue().hashCode();
+	}
 }

samples/boot/oauth2login/src/integration-test/java/org/springframework/security/samples/OAuth2LoginApplicationTests.java

@@ -130,7 +130,7 @@ public class OAuth2LoginApplicationTests {
 
 		Map<String, String> params = uriComponents.getQueryParams().toSingleValueMap();
 
-		assertThat(params.get(OAuth2Parameter.RESPONSE_TYPE)).isEqualTo(ResponseType.CODE.value());
+		assertThat(params.get(OAuth2Parameter.RESPONSE_TYPE)).isEqualTo(ResponseType.CODE.getValue());
 		assertThat(params.get(OAuth2Parameter.CLIENT_ID)).isEqualTo(this.githubClientRegistration.getClientId());
 		String redirectUri = AUTHORIZE_BASE_URL + "/" + this.githubClientRegistration.getClientAlias();
 		assertThat(URLDecoder.decode(params.get(OAuth2Parameter.REDIRECT_URI), "UTF-8")).isEqualTo(redirectUri);