You could create an API with a *path operation* that could trigger a request to an *external API* created by someone else (probably the same developer that would be *using* your API).

The process that happens when your API app calls the *external API* is named a "callback". Because the software that the external developer wrote sends a request to your API and then your API *calls back*, sending a request to an *external API* (that was probably created by the same developer).

`secrets.compare_digest()` needs to take `bytes` or a `str` that only contains ASCII characters (the ones in English), this means it wouldn't work with characters like `á`, as in `Sebastián`.

To handle that, we first convert the `username` and `password` to `bytes` encoding them with UTF-8.

Then we can use `secrets.compare_digest()` to ensure that `credentials.username` is `"stanleyjobson"`, and that `credentials.password` is `"swordfish"`.

///

/// check

The way this dependency system is designed allows us to have different dependencies (different "dependables") that all return a `User` model.

We are not restricted to having only one dependency that can return that type of data.

///

## Other models { #other-models }

     * @param scopesToCollect The dependency scopes that should be collected, may be {@code null}.
     * @param scopesToResolve The dependency scopes that should be collected and also resolved, may be {@code null}.
     * @param session         The current build session, must not be {@code null}.
     * @return The transitive dependencies of the specified project that match the requested scopes, never {@code null}.

        super.tearDown();
    }

    // Test constructor
    public void test_constructor() {
        // Test that constructor creates a non-null instance
        assertNotNull(crawlerEngineClient);
    }

    // Test inheritance
    public void test_inheritance() {
        // Test that CrawlerEngineClient is properly inherited
        assertTrue(crawlerEngineClient instanceof org.codelibs.fess.crawler.client.FesenClient);

Let's imagine that we want to have a dependency that checks if the query parameter `q` contains some fixed content.

But we want to be able to parameterize that fixed content.

## A "callable" instance { #a-callable-instance }

In Python there's a way to make an instance of a class a "callable".

Not the class itself (which is already a callable), but an instance of that class.

# 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**.

The correct place is:

* In the key `content`, that has as value another JSON object (`dict`) that contains:
    * A key with the media type, e.g. `application/json`, that contains as value another JSON object, that contains:
        * A key `schema`, that has as the value the JSON Schema from the model, here's the correct place.

Instead, you want to provide a different dependency that will be used only during tests (possibly only some specific tests), and will provide a value that can be used where the value of the original dependency was used.

### Use cases: external service { #use-cases-external-service }

An example could be that you have an external authentication provider that you need to call.

You send it a token and it returns an authenticated user.

     * <li>If the class loader that loaded the target class can be obtained, that class loader</li>
     * <li>If the class loader that loaded this class can be obtained, that class loader</li>
     * <li>If the system class loader can be obtained, that class loader</li>
     * </ol>
     * <p>