{* ../../docs_src/header_param_models/tutorial001_an_py310.py hl[9:14,18] *}

**FastAPI** will **extract** the data for **each field** from the **headers** in the request and give you the Pydantic model you defined.

## Check the Docs { #check-the-docs }

You can see the required headers in the docs UI at `/docs`:

<div class="screenshot">

   *       instances.
   *   <li>For the constructor or static factory method used to construct instances, it's checked
   *       that when equal parameters are passed, the result instance should also be equal; and vice
   *       versa.
   *   <li>If a non-private constructor or non-private static factory method exists:
   *       <ul>
   *         <li>Test will fail if default value for a parameter cannot be determined.

            @Throws(IOException::class)
            override fun authenticate(route: Route?, response: Response): Request? {
              if (response.request.header("Authorization") != null) {
                return null // Give up, we've already attempted to authenticate.
              }

              println("Authenticating for response: $response")
              println("Challenges: ${response.challenges()}")

{* ../../docs_src/security/tutorial001_an_py39.py hl[12] *}

But that is still not that useful.

Let's make it give us the current user.

## Create a user model { #create-a-user-model }

First, let's create a Pydantic user model.

The same way we use Pydantic to declare bodies, we can use it anywhere else:

    assertEquals(
        thread.getName().substring(0, thread.getName().lastIndexOf('-')),
        thread2.getName().substring(0, thread.getName().lastIndexOf('-')));

    // Building again should give us a different pool ID.
    ThreadFactory threadFactory2 = builder.build();
    Thread thread3 = threadFactory2.newThread(monitoredRunnable);
    checkThreadPoolName(thread3, 1);

   * the table lacks a mapping for a given row and column, the corresponding array element is null.
   *
   * <p>Subsequent table changes will not modify the array, and vice versa.
   *
   * @param valueClass class of values stored in the returned array
   */
  @GwtIncompatible // reflection
  public @Nullable V[][] toArray(Class<V> valueClass) {

import java.util.Iterator;
import java.util.List;
import java.util.Map.Entry;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * A container class for the five sample elements we need for testing.
 *
 * @author Kevin Bourrillion
 */
@GwtCompatible
@NullMarked
public class SampleElements<E extends @Nullable Object> implements Iterable<E> {

- Click `Create subproject` button at the bottom of the "Subprojects" region of [this page](https://builds.gradle.org/admin/editProject.html?projectId=Gradle&tab=projectGeneralTab)
  - Select `Manually`.
  - Give it a name. The name will be displayed on TeamCity web UI. We highly recommend it be capitalized from the branch name, i.e. `MyTestBranch`.

// arena it may have been allocated from, returning the copy. If it was not
// allocated from an arena, it is returned untouched. This function is useful
// to more easily let an arena-allocated value out-live its arena.
// T must be a pointer, a slice, or a string, otherwise this function will panic.
func Clone[T any](s T) T {
	return runtime_arena_heapify(s).(T)
}

//go:linkname reflect_arena_New reflect.arena_New

{* ../../docs_src/cookie_param_models/tutorial001_an_py310.py hl[9:12,16] *}

**FastAPI** will **extract** the data for **each field** from the **cookies** received in the request and give you the Pydantic model you defined.

## Check the Docs { #check-the-docs }

You can see the defined cookies in the docs UI at `/docs`:

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