Fill out JavaDoc for credentialRepositoryV2 and usernameRepository setters

Author: emlun

webauthn-server-core/src/main/java/com/yubico/webauthn/RelyingParty.java

@@ -606,7 +606,12 @@ public RelyingPartyBuilder credentialRepository(CredentialRepository credentialR
 
         /**
          * {@link RelyingPartyBuilder#credentialRepository(CredentialRepository)
-         * credentialRepository} is a required parameter.
+         * credentialRepository} is a required parameter. This setter differs from {@link
+         * #credentialRepository(CredentialRepository)} in that it takes an instance of {@link
+         * CredentialRepositoryV2} and converts the builder's return type to {@link RelyingPartyV2}.
+         * {@link CredentialRepositoryV2} does not require the application to support usernames,
+         * unless {@link RelyingPartyV2.RelyingPartyV2Builder#usernameRepository(UsernameRepository)
+         * usernameRepository} is also set in a subsequent builder step.
          *
          * @see #credentialRepository(CredentialRepository)
          * @deprecated EXPERIMENTAL: This is an experimental feature. It is likely to change or be

webauthn-server-core/src/main/java/com/yubico/webauthn/RelyingPartyV2.java

@@ -140,7 +140,13 @@ public class RelyingPartyV2<C extends CredentialRecord> {
   @NonNull private final CredentialRepositoryV2<C> credentialRepository;
 
   /**
-   * TODO
+   * Enable support for identifying users by username.
+   *
+   * <p>If set, then {@link #startAssertion(StartAssertionOptions)} allows setting the {@link
+   * StartAssertionOptions.StartAssertionOptionsBuilder#username(String) username} parameter when
+   * starting an assertion.
+   *
+   * <p>By default, this is not set.
    *
    * @deprecated EXPERIMENTAL: This is an experimental feature. It is likely to change or be deleted
    *     before reaching a mature release.