# 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 time to answer helps the attackers { #the-time-to-answer-helps-the-attackers }

At that point, by noticing that the server took some microseconds longer to send the "Incorrect username or password" response, the attackers will know that they got _something_ right, some of the initial letters were right.

        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "file:/usr/test/dep.jar")
            .toURI());
    assertEquals(
        new File("/home/build/a.jar").toURI(),
        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "a.jar").toURI());
    assertEquals(
        new File("/home/build/x/y/z").toURI(),
        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "x/y/z").toURI());

## Overriding dependencies during testing { #overriding-dependencies-during-testing }

There are some scenarios where you might want to override a dependency during testing.

You don't want the original dependency to run (nor any of the sub-dependencies it might have).

Asynchronous code just means that the language 💬 has a way to tell the computer / program 🤖 that at some point in the code, it 🤖 will have to wait for *something else* to finish somewhere else. Let's say that *something else* is called "slow-file" 📝.

So, during that time, the computer can go and do some other work, while "slow-file" 📝 finishes.

        netdfs.DfsInfo1 info1 = new netdfs.DfsInfo1();
        info1.entry_path = "test_path";

        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        // Create buffer for encoding - initially allocate some space
        byte[] encodeBuffer = new byte[1024];
        NdrBuffer dst = new NdrBuffer(encodeBuffer, 0);
        info1.encode(dst);

        ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());

</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:

{* ../../docs_src/header_param_models/tutorial002_an_py310.py hl[10] *}

If a client tries to send some **extra headers**, they will receive an **error** response.

**projects depend on**. That's very difficult to manage. And you would probably end up running some projects with some **incompatible versions** of the packages, and not knowing why something isn't working.

Also, depending on your operating system (e.g. Linux, Windows, macOS), it could have come with Python already installed. And in that case it probably had some packages pre-installed with some specific versions **needed by your system**. If you install packages in the global Python environment,...

In this case, it would be better to get **one extra server** and run some processes on it so that they all have **enough RAM and CPU time**.

    * A "token" is just a string with some content that we can use later to verify this user.
    * Normally, a token is set to expire after some time.
        * So, the user will have to log in again at some point later.
        * And if the token is stolen, the risk is less. It is not like a permanent key that will work forever (in most of the cases).