assertEquals(5, chain.deleteCalls.size());
    }

    // Helper method to create test user
    private User createTestUser(String username, String displayName) {
        User user = new User();
        user.setName(username);
        user.setDisplayName(displayName);
        return user;
    }

    // Test implementation of AuthenticationChain for testing

Por ejemplo, en una de las formas en las que se puede usar la especificación OAuth2 (llamada "password flow") se requiere enviar un `username` y `password` como campos de formulario.

La <abbr title="specification">especificación</abbr> requiere que los campos se llamen exactamente `username` y `password`, y que se envíen como campos de formulario, no JSON.

The <abbr title="specification">spec</abbr> requires the fields to be exactly named `username` and `password`, and to be sent as form fields, not JSON.

With `Form` you can declare the same configurations as with `Body` (and `Query`, `Path`, `Cookie`), including validation, examples, an alias (e.g. `user-name` instead of `username`), etc.

/// info

							</c:if>
							<c:choose>
								<c:when test="${!empty username && username != 'guest'}">
									<li class="nav-item">
										<div class="dropdown">
											<a id="userMenu" class="nav-link dropdown-toggle" data-bs-toggle="dropdown"
												href="#" role="button" aria-haspopup="true"
												aria-expanded="false"> <em class="fa fa-fw fa-user">${username}
											</a>

Para manejar eso, primero convertimos el `username` y `password` a `bytes` codificándolos con UTF-8.

Luego podemos usar `secrets.compare_digest()` para asegurar que `credentials.username` es `"stanleyjobson"`, y que `credentials.password` es `"swordfish"`.

{* ../../docs_src/security/tutorial007_an_py39.py hl[1,12:24] *}

Esto sería similar a:

```Python

 * Form for password change.
 */
public class PasswordForm {

    /**
     * Default constructor.
     */
    public PasswordForm() {
        // Default constructor
    }

    /** The username. */
    public String username;

    /** The password. */
    @NotBlank
    public String password;

    /** The confirm password. */
    @NotBlank
    public String confirmPassword;

    /**

            assertEquals("user" + i, chains.get(i).lastLoadedUser.getName());
        }
    }

    // Helper method to create test user
    private User createTestUser(String username) {
        User user = new User();
        user.setName(username);
        return user;
    }

    // Test implementation of AuthenticationChain
    private static class TestAuthenticationChain implements AuthenticationChain {
        int id;

     *
     * @param form the form containing the web authentication data
     * @param username the username of the current user
     * @param currentTime the current timestamp
     * @return an optional WebAuthentication entity
     */
    public static OptionalEntity<WebAuthentication> getEntity(final CreateForm form, final String username, final long currentTime) {
        switch (form.crudMode) {
        case CrudMode.CREATE:

    void delete(User user);

    /**
     * Changes the password for the specified user.
     * @param username The username for which to change the password.
     * @param password The new password.
     * @return True if the password was successfully changed, false otherwise.
     */
    boolean changePassword(String username, String password);

    /**
     * Loads user information from the authentication chain.

        final SystemHelper systemHelper = ComponentUtil.getSystemHelper();
        final String username = systemHelper.getUsername();
        final long currentTime = systemHelper.getCurrentTimeAsLong();
        return getEntity(form, username, currentTime).map(entity -> {
            entity.setUpdatedBy(username);
            entity.setUpdatedTime(currentTime);