# 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**.

## Webhooks steps

#### 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.

* Each application that you have running on your computer has some process behind it, each running program, each window, etc. And there are normally many processes running **at the same time** while a computer is on.
* There can be **multiple processes** of the **same program** running at the same time.

        new File("/home/build/x/y/z.jar").toURI(),
        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "x/y/z.jar").toURI());
    assertEquals(
        "/home/build/x y.jar",
        ClassPath.getClassPathEntry(new File("/home/build/outer.jar"), "x y.jar").getFile());
  }

  public void testGetClassPathFromManifest_nullManifest() {
    assertThat(ClassPath.getClassPathFromManifest(new File("some.jar"), null)).isEmpty();
  }

    * 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).

**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,...

read the main [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

They are all based on the same concepts, but allow some extra functionalities....

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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.

### Certificate Renewal

At some point in the future, each certificate would **expire** (about 3 months after acquiring it).

And then, there would be another program (in some cases it's another program, in some cases it could be the same TLS Termination Proxy) that would talk to Let's Encrypt, and renew the certificate(s).