Allow URL-specific avatar image sources in CSP

core/src/main/java/jenkins/security/csp/AvatarContributor.java

@@ -27,6 +27,7 @@
 import edu.umd.cs.findbugs.annotations.CheckForNull;
 import hudson.Extension;
 import hudson.ExtensionList;
+import java.net.IDN;
 import java.net.URI;
 import java.net.URISyntaxException;
 import java.util.Locale;
@@ -48,10 +49,12 @@
     private static final Logger LOGGER = Logger.getLogger(AvatarContributor.class.getName());
 
     private final Set<String> domains = ConcurrentHashMap.newKeySet();
+    private final Set<String> allowedSources = ConcurrentHashMap.newKeySet();
 
     @Override
     public void apply(CspBuilder cspBuilder) {
         domains.forEach(d -> cspBuilder.add("img-src", d));
+        allowedSources.forEach(s -> cspBuilder.add("img-src", s));
     }
 
     /**
@@ -84,6 +87,29 @@
         }
     }
 
+    /**
+     * Request addition of a specific URL to the allowed set of avatar sources.
+     * This method allows external plugins to allowlist specific image URLs so they can be loaded via CSP.
+     *
+     * @param url The full avatar image URL to allow.
+     */
+    @SuppressWarnings("unused")
+    public static void allowUrl(@CheckForNull String url) {
+        AvatarContributor self = ExtensionList.lookupSingleton(AvatarContributor.class);
+
+        if (addNormalizedUrl(url, self.allowedSources)) {
+            LOGGER.log(Level.CONFIG, "Adding allowed avatar URL: {0}", url);
+        }
+    }
+
+    static boolean addNormalizedUrl(@CheckForNull String url, Set<String> target) {
+        String normalized = normalizeUrl(url);
+        if (normalized == null) {
+            return false;
+        }
+        return target.add(normalized);
+    }
+
     /**
      * Utility method extracting the domain specification for CSP fetch directives from a specified URL.
      * If the specified URL is not {@code null}, has a host, and {@code http} or {@code https} scheme, this method
@@ -128,4 +154,111 @@
             return null;
         }
     }
+
+    /**
+     * Normalizes a URL for use in Content-Security-Policy.
+     * <p>
+     * This method validates and canonicalizes the URL to ensure it is safe for use in a CSP header.
+     * </p>
+     * <ul>
+     *   <li>
+     *     <strong>Accepts only http and https schemes</strong> -
+     *     Avatar images are fetched over the network. Other schemes such as file, data, or JavaScript are either unsafe
+     *     or meaningless in a CSP img-src context.
+     *   </li>
+     *   <li>
+     *     <strong>Rejects URLs with embedded credentials</strong> —
+     *     URLs containing user:password@host can accidentally expose credentials in logs or browser requests. Such URLs
+     *     are then rejected.
+     *   </li>
+     *   <li>
+     *     <strong>Converts IDN to ASCII</strong> —
+     *     Browser internally normalize hostnames to their ASCII representation. Normalizing here ensures Jenkins
+     *     generates CSP entries that match browser behavior consistently.
+     *   </li>
+     *   <li>
+     *     <strong>Normalizes IPv6 literals</strong> —
+     *     IPv6 addresses must be enclosed in square brackets in URLs.
+     *   </li>
+     *   <li>
+     *     <strong>Removes default ports</strong> —
+     *     Ports  80 (HTTP) and 443 (HTTPS) are removed. Removing them avoids duplicate CSP entries that differ only
+     *     by the presence of a default port.
+     *   </li>
+     * </ul>
+     *
+     * @param url The raw input URL.
+     * @return A canonical, safe string representation of the URL, or null if the URL is invalid or unsafe.
+     */
+    @CheckForNull
+    public static String normalizeUrl(@CheckForNull String url) {
+        if (url == null) {
+            return null;
+        }
+        try {
+            URI uri = new URI(url);
+
+            String scheme = uri.getScheme();
+            if (scheme == null) {
+                LOGGER.log(Level.FINER, "Ignoring URI without scheme: " + url);
+                return null;
+            }
+            scheme = scheme.toLowerCase(Locale.ROOT);
+            if (!scheme.equals("http") && !scheme.equals("https")) {
+                LOGGER.log(Level.FINER, "Ignoring URI with unsupported scheme: " + url);
+                return null;
+            }
+
+            if (uri.getUserInfo() != null && !uri.getUserInfo().isEmpty()) {
+                LOGGER.log(Level.FINER, "Ignoring URI with embedded credentials: " + url);
+                return null;
+            }
+
+            String rawAuthority = uri.getRawAuthority();
+            if (rawAuthority == null) {
+                LOGGER.log(Level.FINER, "Ignoring URI without authority: " + url);
+                return null;
+            }
+
+            String host;
+            int port = uri.getPort();
+
+            if (rawAuthority.startsWith("[")) {
+                int end = rawAuthority.indexOf(']');
+                if (end == -1) {
+                    return null;
+                }
+                host = rawAuthority.substring(1, end);
+            } else {
+                int colon = rawAuthority.indexOf(':');
+                host = colon >= 0 ? rawAuthority.substring(0, colon) : rawAuthority;
+            }
+
+            String asciiHost = IDN.toASCII(host).toLowerCase(Locale.ROOT);
+            boolean ipv6 = asciiHost.contains(":");
+            String hostPart = ipv6 ? "[" + asciiHost + "]" : asciiHost;
+
+            boolean omitPort =
+                port == -1 ||
+                    (scheme.equals("http") && port == 80) ||
+                    (scheme.equals("https") && port == 443);
+
+            String portPart = omitPort ? "" : ":" + port;
+
+            String path = uri.getRawPath();
+            if (path == null || path.isEmpty()) {
+                path = "/";
+            }
+
+            String query = uri.getRawQuery();
+            String queryPart = query == null || query.isEmpty() ? "" : "?" + query;
+
+            return scheme + "://" + hostPart + portPart + path + queryPart;
+
+        } catch (URISyntaxException | IllegalArgumentException e) {
+            LOGGER.log(Level.FINE, "Failed to normalize avatar URI: " + url, e);
+            return null;
+        }
+    }
+
 }

core/src/test/java/jenkins/security/csp/AvatarContributorTest.java

@@ -2,9 +2,15 @@
 
 import static jenkins.security.csp.AvatarContributor.extractDomainFromUrl;
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.nullValue;
+import static org.hamcrest.Matchers.startsWith;
 
+import java.util.HashSet;
+import java.util.Set;
 import org.junit.jupiter.api.Test;
 import org.jvnet.hudson.test.For;
 
@@ -85,4 +91,109 @@ void testExtractDomainFromUrl_Ipv4WithPort() {
     void testExtractDomainFromUrl_CaseInsensitivity() {
         assertThat(extractDomainFromUrl("hTTps://EXAMPLE.com/path/to/avatar.png"), is("https://example.com"));
     }
+
+    @Test
+    void testNormalizeUrl_BasicHttps() {
+        assertThat(
+            AvatarContributor.normalizeUrl("https://example.com/avatars/u1.png"), is("https://example.com/avatars/u1.png")
+        );
+    }
+
+    @Test
+    void testNormalizeUrl_PreservesEncodedPathAndQuery() {
+        assertThat(
+            AvatarContributor.normalizeUrl("https://example.com/a%20b.png?size=64"), is("https://example.com/a%20b.png?size=64")
+        );
+    }
+
+    @Test
+    void testNormalizeUrl_StripsFragment() {
+        assertThat(
+            AvatarContributor.normalizeUrl("https://example.com/a.png#fragment"), is("https://example.com/a.png")
+        );
+    }
+
+    @Test
+    void testNormalizeUrl_RejectsUserInfo() {
+        assertThat(
+            AvatarContributor.normalizeUrl("https://user:pass@example.com/a.png"), is(nullValue())
+        );
+    }
+
+    @Test
+    void testNormalizeUrl_RejectsUnsupportedScheme() {
+        assertThat(
+            AvatarContributor.normalizeUrl("ftp://example.com/a.png"), is(nullValue())
+        );
+    }
+
+    @Test
+    void testNormalizeUrl_OmitsDefaultHttpsPort() {
+        assertThat(
+            AvatarContributor.normalizeUrl("https://example.com:443/a.png"), is("https://example.com/a.png")
+        );
+    }
+
+    @Test
+    void testNormalizeUrl_OmitsDefaultHttpPort() {
+        assertThat(
+            AvatarContributor.normalizeUrl("http://example.com:80/a.png"), is("http://example.com/a.png")
+        );
+    }
+
+    @Test
+    void testNormalizeUrl_KeepsNonDefaultPort() {
+        assertThat(
+            AvatarContributor.normalizeUrl("https://example.com:8443/a.png"), is("https://example.com:8443/a.png")
+        );
+    }
+
+    // This test does not assert the exact full string. Its purpose is to verify that IPv6 literals are correctly bracketed,
+    // while the path and other components are covered by separate tests.
+    @Test
+    void testNormalizeUrl_Ipv6HostIsBracketed() {
+        String normalized = AvatarContributor.normalizeUrl("https://[2001:db8::1]/a.png");
+        assertThat(normalized, startsWith("https://[2001:db8::1]"));
+        assertThat(normalized, containsString("/a.png"));
+    }
+
+    // Verifies that the Unicode hostname is converted to its ASCII representation while preserving the
+    // rest of the URL structure.
+    @Test
+    void testNormalizeUrl_IdnIsConvertedToAscii() {
+        String normalized = AvatarContributor.normalizeUrl("https://例え.テスト/a.png");
+        assertThat(normalized, startsWith("https://xn--r8jz45g.xn--zckzah"));
+    }
+
+    @Test
+    void testAddNormalizedUrl_AddsValidUrl() {
+        Set<String> set = new HashSet<>();
+
+        boolean added = AvatarContributor.addNormalizedUrl("https://example.com/a.png", set);
+
+        assertThat(added, is(true));
+        assertThat(set, contains("https://example.com/a.png"));
+    }
+
+    @Test
+    void testAddNormalizedUrl_RejectsInvalidUrl() {
+        Set<String> set = new HashSet<>();
+
+        boolean added = AvatarContributor.addNormalizedUrl("ftp://example.com/a.png", set);
+
+        assertThat(added, is(false));
+        assertThat(set, empty());
+    }
+
+    @Test
+    void testAddNormalizedUrl_Deduplicates() {
+        Set<String> set = new HashSet<>();
+
+        AvatarContributor.addNormalizedUrl("https://example.com/a.png", set);
+        boolean addedAgain = AvatarContributor.addNormalizedUrl("https://example.com/a.png", set);
+
+        assertThat(addedAgain, is(false));
+        assertThat(set.size(), is(1));
+    }
+
 }