Allow "*" for Access-Control-Expose-Headers

Closes gh-26113

Author: rstoyanchev

spring-web/src/main/java/org/springframework/web/bind/annotation/CrossOrigin.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * 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.
@@ -112,6 +112,8 @@
 	 * {@code Expires}, {@code Last-Modified}, or {@code Pragma},
 	 * <p>Exposed headers are listed in the {@code Access-Control-Expose-Headers}
 	 * response header of actual CORS requests.
+	 * <p>The special value {@code "*"} allows all headers to be exposed for
+	 * non-credentialed requests.
 	 * <p>By default no headers are listed as exposed.
 	 */
 	String[] exposedHeaders() default {};

spring-web/src/main/java/org/springframework/web/cors/CorsConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * 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.
@@ -253,13 +253,11 @@ else if (this.allowedHeaders == DEFAULT_PERMIT_ALL) {
 	 * {@code Cache-Control}, {@code Content-Language}, {@code Content-Type},
 	 * {@code Expires}, {@code Last-Modified}, or {@code Pragma}) that an
 	 * actual response might have and can be exposed.
-	 * <p>Note that {@code "*"} is not a valid exposed header value.
+	 * <p>The special value {@code "*"} allows all headers to be exposed for
+	 * non-credentialed requests.
 	 * <p>By default this is not set.
 	 */
 	public void setExposedHeaders(@Nullable List<String> exposedHeaders) {
-		if (exposedHeaders != null && exposedHeaders.contains(ALL)) {
-			throw new IllegalArgumentException("'*' is not a valid exposed header value");
-		}
 		this.exposedHeaders = (exposedHeaders != null ? new ArrayList<>(exposedHeaders) : null);
 	}
 
@@ -275,12 +273,10 @@ public List<String> getExposedHeaders() {
 
 	/**
 	 * Add a response header to expose.
-	 * <p>Note that {@code "*"} is not a valid exposed header value.
+	 * <p>The special value {@code "*"} allows all headers to be exposed for
+	 * non-credentialed requests.
 	 */
 	public void addExposedHeader(String exposedHeader) {
-		if (ALL.equals(exposedHeader)) {
-			throw new IllegalArgumentException("'*' is not a valid exposed header value");
-		}
 		if (this.exposedHeaders == null) {
 			this.exposedHeaders = new ArrayList<>(4);
 		}

spring-web/src/test/java/org/springframework/web/cors/CorsConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * 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.
@@ -60,27 +60,14 @@ public void setValues() {
 		assertEquals(Arrays.asList("*"), config.getAllowedHeaders());
 		config.addAllowedMethod("*");
 		assertEquals(Arrays.asList("*"), config.getAllowedMethods());
-		config.addExposedHeader("header1");
-		config.addExposedHeader("header2");
-		assertEquals(Arrays.asList("header1", "header2"), config.getExposedHeaders());
+		config.addExposedHeader("*");
+		assertEquals(Arrays.asList("*"), config.getAllowedMethods());
 		config.setAllowCredentials(true);
 		assertTrue(config.getAllowCredentials());
 		config.setMaxAge(123L);
 		assertEquals(new Long(123), config.getMaxAge());
 	}
 
-	@Test(expected = IllegalArgumentException.class)
-	public void asteriskWildCardOnAddExposedHeader() {
-		CorsConfiguration config = new CorsConfiguration();
-		config.addExposedHeader("*");
-	}
-
-	@Test(expected = IllegalArgumentException.class)
-	public void asteriskWildCardOnSetExposedHeaders() {
-		CorsConfiguration config = new CorsConfiguration();
-		config.setExposedHeaders(Arrays.asList("*"));
-	}
-
 	@Test
 	public void combineWithNull() {
 		CorsConfiguration config = new CorsConfiguration();
@@ -120,43 +107,52 @@ public void combineWithDefaultPermitValues() {
 		assertEquals(Arrays.asList("https://domain.com"), combinedConfig.getAllowedOrigins());
 		assertEquals(Arrays.asList("header1"), combinedConfig.getAllowedHeaders());
 		assertEquals(Arrays.asList(HttpMethod.PUT.name()), combinedConfig.getAllowedMethods());
+		assertEquals(Collections.emptyList(), combinedConfig.getExposedHeaders());
 
 		combinedConfig = other.combine(config);
 		assertEquals(Arrays.asList("https://domain.com"), combinedConfig.getAllowedOrigins());
 		assertEquals(Arrays.asList("header1"), combinedConfig.getAllowedHeaders());
 		assertEquals(Arrays.asList(HttpMethod.PUT.name()), combinedConfig.getAllowedMethods());
+		assertEquals(Collections.emptyList(), combinedConfig.getExposedHeaders());
 
 		combinedConfig = config.combine(new CorsConfiguration());
 		assertEquals(Arrays.asList("*"), config.getAllowedOrigins());
 		assertEquals(Arrays.asList("*"), config.getAllowedHeaders());
 		assertEquals(Arrays.asList(HttpMethod.GET.name(), HttpMethod.HEAD.name(),
 				HttpMethod.POST.name()), combinedConfig.getAllowedMethods());
+		assertEquals(Collections.emptyList(), combinedConfig.getExposedHeaders());
 
 		combinedConfig = new CorsConfiguration().combine(config);
 		assertEquals(Arrays.asList("*"), config.getAllowedOrigins());
 		assertEquals(Arrays.asList("*"), config.getAllowedHeaders());
 		assertEquals(Arrays.asList(HttpMethod.GET.name(), HttpMethod.HEAD.name(),
 				HttpMethod.POST.name()), combinedConfig.getAllowedMethods());
+		assertEquals(Collections.emptyList(), combinedConfig.getExposedHeaders());
 	}
 
 	@Test
 	public void combineWithAsteriskWildCard() {
 		CorsConfiguration config = new CorsConfiguration();
 		config.addAllowedOrigin("*");
 		config.addAllowedHeader("*");
+		config.addExposedHeader("*");
 		config.addAllowedMethod("*");
 		CorsConfiguration other = new CorsConfiguration();
 		other.addAllowedOrigin("https://domain.com");
 		other.addAllowedHeader("header1");
 		other.addExposedHeader("header2");
+		other.addAllowedHeader("anotherHeader1");
+		other.addExposedHeader("anotherHeader2");
 		other.addAllowedMethod(HttpMethod.PUT.name());
 		CorsConfiguration combinedConfig = config.combine(other);
 		assertEquals(Arrays.asList("*"), combinedConfig.getAllowedOrigins());
 		assertEquals(Arrays.asList("*"), combinedConfig.getAllowedHeaders());
+		assertEquals(Arrays.asList("*"), combinedConfig.getExposedHeaders());
 		assertEquals(Arrays.asList("*"), combinedConfig.getAllowedMethods());
 		combinedConfig = other.combine(config);
 		assertEquals(Arrays.asList("*"), combinedConfig.getAllowedOrigins());
 		assertEquals(Arrays.asList("*"), combinedConfig.getAllowedHeaders());
+		assertEquals(Arrays.asList("*"), combinedConfig.getExposedHeaders());
 		assertEquals(Arrays.asList("*"), combinedConfig.getAllowedMethods());
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/config/CorsRegistration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * 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.
@@ -93,7 +93,8 @@ public CorsRegistration allowedHeaders(String... headers) {
 	 * {@code Cache-Control}, {@code Content-Language}, {@code Content-Type},
 	 * {@code Expires}, {@code Last-Modified}, or {@code Pragma}, that an
 	 * actual response might have and can be exposed.
-	 * <p>Note that {@code "*"} is not supported on this property.
+	 * <p>The special value {@code "*"} allows all headers to be exposed for
+	 * non-credentialed requests.
 	 * <p>By default this is not set.
 	 */
 	public CorsRegistration exposedHeaders(String... headers) {

spring-webmvc/src/main/java/org/springframework/web/servlet/config/annotation/CorsRegistration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * 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.
@@ -95,7 +95,8 @@ public CorsRegistration allowedHeaders(String... headers) {
 	 * {@code Cache-Control}, {@code Content-Language}, {@code Content-Type},
 	 * {@code Expires}, {@code Last-Modified}, or {@code Pragma}, that an
 	 * actual response might have and can be exposed.
-	 * <p>Note that {@code "*"} is not supported on this property.
+	 * <p>The special value {@code "*"} allows all headers to be exposed for
+	 * non-credentialed requests.
 	 * <p>By default this is not set.
 	 */
 	public CorsRegistration exposedHeaders(String... headers) {

spring-webmvc/src/main/resources/org/springframework/web/servlet/config/spring-mvc.xsd

@@ -1363,6 +1363,7 @@
 	Comma-separated list of response headers other than simple headers (i.e.
 	Cache-Control, Content-Language, Content-Type, Expires, Last-Modified, Pragma) that an
 	actual response might have and can be exposed.
+	The special value "*" allows all headers to be exposed for non-credentialed requests.
 	Empty by default.
 								]]></xsd:documentation>
 							</xsd:annotation>