<div class="screenshot">
<img src="/img/tutorial/header-param-models/image01.png">
</div>

## Forbid Extra Headers { #forbid-extra-headers }

In some special use cases (probably not very common), you might want to **restrict** the headers that you want to receive.

You can use Pydantic's model configuration to `forbid` any `extra` fields:

# OpenAPI Webhooks { #openapi-webhooks }

There are cases where you want to tell your API **users** that your app could call *their* app (sending a request) with some data, normally to **notify** of some type of **event**.

This means that instead of the normal process of your users sending requests to your API, it's **your API** (or your app) that could **send requests to their system** (to their API, their app).

This is normally called a **webhook**.

For example, you cannot put a Pydantic model in a `JSONResponse` without first converting it to a `dict` with all the data types (like `datetime`, `UUID`, etc) converted to JSON-compatible types.

For those cases, you can use the `jsonable_encoder` to convert your data before passing it to a response:

{* ../../docs_src/response_directly/tutorial001.py hl[6:7,21:22] *}

/// note | Technical Details

/**
 * Tests for SMBProtocolDowngradeException covering all constructors and behaviors.
 */
@ExtendWith(MockitoExtension.class)
class SMBProtocolDowngradeExceptionTest {

    /**
     * Provides messages including edge cases (null and empty) for parameterized testing.
     */
    static Stream<Arguments> messages() {
        return Stream.of(Arguments.of((String) null), Arguments.of(""), Arguments.of("unexpected downgrade"));
    }

    @Test

        assertEscaping(xmlEscaper, "\uFFFD", ch);
      }
    }

    // Test _all_ allowed characters (including surrogate values).
    for (char ch = 0x20; ch <= 0xFFFD; ch++) {
      // There are a small number of cases to consider, so just do it manually.
      if (ch == '&') {
        assertEscaping(xmlEscaper, "&amp;", ch);
      } else if (ch == '<') {
        assertEscaping(xmlEscaper, "&lt;", ch);
      } else if (ch == '>') {

            // Don't assert true/false here, just test that method doesn't throw
            assertNotNull("Validation should return a boolean result for: " + cron, Boolean.valueOf(result));
        }
    }

    // Test edge cases to understand the validation behavior
    public void test_edgeCaseBehavior() {
        String[] edgeCases = { "0 0 25 * * ?", // Invalid day of month
                "0 60 * * * ?", // Invalid minute

 * is a thin wrapper around {@link InetAddresses} and {@link InternetDomainName}; the unit tests for
 * those classes explore numerous corner cases. The intent here is to confirm that everything is
 * wired up properly.
 *
 * @author Craig Berry
 */
@NullUnmarked
public final class HostSpecifierTest extends TestCase {

 *
 * <p>{@code UncheckedExecutionException} is intended as an alternative to {@code
 * ExecutionException} when the exception thrown by a task is an unchecked exception. However, it
 * may also wrap a checked exception in some cases.
 *
 * <p>When wrapping an {@code Error} from another thread, prefer {@link ExecutionError}. When
 * wrapping a checked exception, prefer {@code ExecutionException}.
 *
 * @author Charles Fry
 * @since 10.0
 */

            // Then
            assertEquals(443, httpsPort);
            assertEquals(80, httpPort);
            assertNotEquals(httpsPort, httpPort);
        }
    }

    @Nested
    @DisplayName("Edge Cases")
    class EdgeCaseTests {

        @Test
        @DisplayName("Should handle reflection access to protected method")
        void testProtectedMethodAccess() throws Exception {
            // Given

### Tags with Enums { #tags-with-enums }

If you have a big application, you might end up accumulating **several tags**, and you would want to make sure you always use the **same tag** for related *path operations*.

In these cases, it could make sense to store the tags in an `Enum`.

**FastAPI** supports that the same way as with plain strings:

{* ../../docs_src/path_operation_configuration/tutorial002b.py hl[1,8:10,13,18] *}