[JENKINS-43852] add caching options for captcha (#3126)

* JENKINS-42852 add caching options for captcha

* - remove whitespace

* - correct unit tests

* - copy/paste is bad

* - second edit...

(cherry picked from commit 80d17f5a68)

core/src/main/java/hudson/security/SecurityRealm.java

@@ -402,7 +402,10 @@ public abstract class SecurityRealm extends AbstractDescribableImpl<SecurityReal
         if (captchaSupport != null) {
             String id = req.getSession().getId();
             rsp.setContentType("image/png");
-            rsp.addHeader("Cache-Control", "no-cache");
+            // source: https://stackoverflow.com/a/3414217
+            rsp.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
+            rsp.setHeader("Pragma", "no-cache");
+            rsp.setHeader("Expires", "0");
             captchaSupport.generateImage(id, rsp.getOutputStream());
         }
     }

test/src/test/java/hudson/security/SecurityRealmTest.java

@@ -0,0 +1,82 @@
+/*
+ * The MIT License
+ *
+ * Copyright (c) 2017, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package hudson.security;
+
+import com.gargoylesoftware.htmlunit.WebResponse;
+import com.gargoylesoftware.htmlunit.util.NameValuePair;
+import hudson.security.captcha.CaptchaSupport;
+import org.hamcrest.CoreMatchers;
+import org.junit.Rule;
+import org.junit.Test;
+import org.jvnet.hudson.test.Issue;
+import org.jvnet.hudson.test.JenkinsRule;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThat;
+
+public class SecurityRealmTest {
+
+    @Rule
+    public JenkinsRule j = new JenkinsRule();
+
+    @Test
+    @Issue("JENKINS-43852")
+    public void testCacheHeaderInResponse() throws Exception {
+        SecurityRealm securityRealm = j.createDummySecurityRealm();
+        j.jenkins.setSecurityRealm(securityRealm);
+
+        WebResponse response = j.createWebClient()
+                .goTo("securityRealm/captcha", "")
+                .getWebResponse();
+        assertEquals(response.getContentAsString(), "");
+
+        securityRealm.setCaptchaSupport(new DummyCaptcha());
+
+        response = j.createWebClient()
+                .goTo("securityRealm/captcha", "image/png")
+                .getWebResponse();
+
+        assertThat(response.getResponseHeaderValue("Cache-Control"), is("no-cache, no-store, must-revalidate"));
+        assertThat(response.getResponseHeaderValue("Pragma"), is("no-cache"));
+        assertThat(response.getResponseHeaderValue("Expires"), is("0"));
+    }
+
+    private class DummyCaptcha extends CaptchaSupport {
+        @Override
+        public boolean validateCaptcha(String id, String text) {
+            return false;
+        }
+
+        @Override
+        public void generateImage(String id, OutputStream ios) throws IOException {
+        }
+    }
+}