To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

Let's use the tools provided by **FastAPI** to handle security.

## How it looks { #how-it-looks }

Let's first just use the code and see how it works, and then we'll come back to understand what's happening.

## Create `main.py` { #create-main-py }

Copy the example in a file `main.py`:

{* ../../docs_src/security/tutorial001_an_py39.py *}

## Run it { #run-it }

/// info

    Iterator<Integer> it = mmHeap.iterator();
    assertEquals((Integer) 1, it.next());
    assertEquals((Integer) 20, it.next());
    assertEquals((Integer) 100, it.next());
    assertEquals((Integer) 2, it.next());
    it.remove();
    assertFalse(mmHeap.contains(2));
    assertTrue(it.hasNext());
    assertEquals((Integer) 3, it.next());
    assertTrue(it.hasNext());

will burn you if you hold it too long; and that if you cut your
finger VERY deeply with a knife, it usually bleeds; and she had
never forgotten that, if you drink much from a bottle marked
`poison,' it is almost certain to disagree with you, sooner or
later.

  However, this bottle was NOT marked `poison,' so Alice ventured
to taste it, and finding it very nice, (it had, in fact, a sort

If you want to secure your API, there are several better things you can do, for example:

* Make sure you have well defined Pydantic models for your request bodies and responses.

      stack.addFirst(closeable);
    }

    return closeable;
  }

  /**
   * Stores the given throwable and rethrows it. It will be rethrown as is if it is an {@code
   * IOException}, {@code RuntimeException} or {@code Error}. Otherwise, it will be rethrown wrapped
   * in a {@code RuntimeException}. <b>Note:</b> Be sure to declare all of the checked exception

    #   o isReplaceSchemaDirectUse: Does it output the data to playsql directly? (NotRequired - Default false)
    #   o isOverrideExistingDataFile: Does it output to existing files? (NotRequired - Default false)
    #   o isSynchronizeOriginDate: Does it synchronize origin date for date adjustment? (NotRequired - Default false)
    #
    ; loadDataReverseMap = map:{

## About JWT { #about-jwt }

JWT means "JSON Web Tokens".

It's a standard to codify a JSON object in a long dense string without spaces. It looks like this:

```
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
```

/// tip

...Although if the whole application is just **crashing immediately** it probably doesn't make sense to keep restarting it forever. But in those cases, you will probably notice it during development, or at least right after deployment.

So let's focus on the main cases, where it could crash entirely in some particular cases **in the future**, and it still makes sense to restart it.

///

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