Add some missing JavaDocs for extensions

Author: emlun

webauthn-server-core/src/main/java/com/yubico/webauthn/data/ClientAssertionExtensionOutputs.java

@@ -98,6 +98,16 @@ public Optional<Boolean> getAppid() {
     return Optional.ofNullable(appid);
   }
 
+  /**
+   * The extension output for the <a
+   * href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-large-blob-extension">Large blob
+   * storage (<code>largeBlob</code>) extension</a>, if any.
+   *
+   * @see com.yubico.webauthn.data.Extensions.LargeBlob.LargeBlobRegistrationOutput
+   * @see <a
+   *     href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-large-blob-extension">§10.5.Large
+   *     blob storage extension (largeBlob)</a>
+   */
   public Optional<Extensions.LargeBlob.LargeBlobAuthenticationOutput> getLargeBlob() {
     return Optional.ofNullable(largeBlob);
   }

webauthn-server-core/src/main/java/com/yubico/webauthn/data/ClientRegistrationExtensionOutputs.java

@@ -87,6 +87,18 @@ public Set<String> getExtensionIds() {
     return ids;
   }
 
+  /**
+   * The extension output for the <a
+   * href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-appid-exclude-extension">FIDO
+   * AppID Exclusion (<code>appidExclude</code>) Extension</a>, if any.
+   *
+   * <p>This value is generally not useful, as it only communicates whether the client supports the
+   * extension.
+   *
+   * @see <a
+   *     href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-appid-exclude-extension">§10.2.FIDO
+   *     AppID Exclusion Extension (appidExclude)</a>
+   */
   public Optional<Boolean> getAppidExclude() {
     return Optional.ofNullable(appidExclude);
   }

webauthn-server-core/src/main/java/com/yubico/webauthn/data/Extensions.java

@@ -19,14 +19,28 @@
 import lombok.experimental.UtilityClass;
 import lombok.extern.slf4j.Slf4j;
 
+/** Definitions for WebAuthn extensions. */
 @Slf4j
 @UtilityClass
 public class Extensions {
 
+  /**
+   * Definitions for the FIDO AppID Extension (<code>appid</code>).
+   *
+   * @see <a href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-appid-extension">§10.1.
+   *     FIDO AppID Extension (appid)</a>
+   */
   public static class Appid {
     public static final String EXTENSION_ID = "appid";
   }
 
+  /**
+   * Definitions for the 10.2. FIDO AppID Exclusion Extension (<code>appidExclude</code>).
+   *
+   * @see <a
+   *     href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-appid-exclude-extension">10.2.
+   *     FIDO AppID Exclusion Extension (appidExclude)</a>
+   */
   public static class AppidExclude {
     public static final String EXTENSION_ID = "appidExclude";
   }
@@ -373,8 +387,19 @@ public Optional<Boolean> getWritten() {
    *     User Verification Method Extension (uvm)</a>
    */
   public static class Uvm {
-    public static final String EXTENSION_ID = "uvm";
+    static final String EXTENSION_ID = "uvm";
 
+    /**
+     * A <code>uvmEntry</code> as defined in <a
+     * href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-uvm-extension">§10.3. User
+     * Verification Method Extension (uvm)</a>.
+     *
+     * @see <a href="https://www.w3.org/TR/2021/REC-webauthn-2-20210408/#sctn-uvm-extension">§10.3.
+     *     User Verification Method Extension (uvm)</a>
+     * @see UserVerificationMethod
+     * @see KeyProtectionType
+     * @see MatcherProtectionType
+     */
     @Value
     public static class UvmEntry {
       private final UserVerificationMethod userVerificationMethod;