Authorization Consent request state parameter is validated

Closes gh-503

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2AuthorizationCodeRequestAuthenticationConverter.java

@@ -118,11 +118,20 @@ public final class OAuth2AuthorizationCodeRequestAuthenticationConverter impleme
 			}
 		}
 
-		// state (RECOMMENDED)
+		// state
+		// RECOMMENDED for Authorization Request
 		String state = parameters.getFirst(OAuth2ParameterNames.STATE);
-		if (StringUtils.hasText(state) &&
-				parameters.get(OAuth2ParameterNames.STATE).size() != 1) {
-			throwError(OAuth2ErrorCodes.INVALID_REQUEST, OAuth2ParameterNames.STATE);
+		if (authorizationRequest) {
+			if (StringUtils.hasText(state) &&
+					parameters.get(OAuth2ParameterNames.STATE).size() != 1) {
+				throwError(OAuth2ErrorCodes.INVALID_REQUEST, OAuth2ParameterNames.STATE);
+			}
+		} else {
+			// REQUIRED for Authorization Consent Request
+			if (!StringUtils.hasText(state) ||
+					parameters.get(OAuth2ParameterNames.STATE).size() != 1) {
+				throwError(OAuth2ErrorCodes.INVALID_REQUEST, OAuth2ParameterNames.STATE);
+			}
 		}
 
 		// code_challenge (REQUIRED for public clients) - RFC 7636 (PKCE)

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/OAuth2AuthorizationEndpointFilterTests.java

@@ -222,6 +222,24 @@ public class OAuth2AuthorizationEndpointFilterTests {
 				request -> request.addParameter(OAuth2ParameterNames.STATE, "state2"));
 	}
 
+	@Test
+	public void doFilterWhenAuthorizationConsentRequestMissingStateThenInvalidRequestError() throws Exception {
+		doFilterWhenAuthorizationConsentRequestInvalidParameterThenError(
+				TestRegisteredClients.registeredClient().build(),
+				OAuth2ParameterNames.STATE,
+				OAuth2ErrorCodes.INVALID_REQUEST,
+				request -> request.removeParameter(OAuth2ParameterNames.STATE));
+	}
+
+	@Test
+	public void doFilterWhenAuthorizationConsentRequestMultipleStateThenInvalidRequestError() throws Exception {
+		doFilterWhenAuthorizationConsentRequestInvalidParameterThenError(
+				TestRegisteredClients.registeredClient().build(),
+				OAuth2ParameterNames.STATE,
+				OAuth2ErrorCodes.INVALID_REQUEST,
+				request -> request.addParameter(OAuth2ParameterNames.STATE, "state2"));
+	}
+
 	@Test
 	public void doFilterWhenAuthorizationRequestMultipleCodeChallengeThenInvalidRequestError() throws Exception {
 		doFilterWhenAuthorizationRequestInvalidParameterThenError(
@@ -534,6 +552,13 @@ public class OAuth2AuthorizationEndpointFilterTests {
 				parameterName, errorCode, requestConsumer);
 	}
 
+	private void doFilterWhenAuthorizationConsentRequestInvalidParameterThenError(RegisteredClient registeredClient,
+			String parameterName, String errorCode, Consumer<MockHttpServletRequest> requestConsumer) throws Exception {
+
+		doFilterWhenRequestInvalidParameterThenError(createAuthorizationConsentRequest(registeredClient),
+				parameterName, errorCode, requestConsumer);
+	}
+
 	private void doFilterWhenRequestInvalidParameterThenError(MockHttpServletRequest request,
 			String parameterName, String errorCode, Consumer<MockHttpServletRequest> requestConsumer) throws Exception {
 
@@ -564,6 +589,18 @@ public class OAuth2AuthorizationEndpointFilterTests {
 		return request;
 	}
 
+	private static MockHttpServletRequest createAuthorizationConsentRequest(RegisteredClient registeredClient) {
+		String requestUri = DEFAULT_AUTHORIZATION_ENDPOINT_URI;
+		MockHttpServletRequest request = new MockHttpServletRequest("POST", requestUri);
+		request.setServletPath(requestUri);
+
+		request.addParameter(OAuth2ParameterNames.CLIENT_ID, registeredClient.getClientId());
+		registeredClient.getScopes().forEach((scope) -> request.addParameter(OAuth2ParameterNames.SCOPE, scope));
+		request.addParameter(OAuth2ParameterNames.STATE, "state");
+
+		return request;
+	}
+
 	private static OAuth2AuthorizationCodeRequestAuthenticationToken.Builder authorizationCodeRequestAuthentication(
 			RegisteredClient registeredClient, Authentication principal) {
 		return OAuth2AuthorizationCodeRequestAuthenticationToken.with(registeredClient.getClientId(), principal)