And **your users** define in some way (for example in a web dashboard somewhere) the **URL** where your app should send those requests.

All the **logic** about how to register the URLs for webhooks and the code to actually send those requests is up to you. You write it however you want to in **your own code**.

## Documenting webhooks with **FastAPI** and OpenAPI

    "Topic :: Internet :: WWW/HTTP",
]
dependencies = [
    "starlette>=0.37.2,<0.38.0",
    "pydantic>=1.7.4,!=1.8,!=1.8.1,!=2.0.0,!=2.0.1,!=2.1.0,<3.0.0",
    "typing-extensions>=4.8.0",
]

[project.urls]
Homepage = "https://github.com/tiangolo/fastapi"
Documentation = "https://fastapi.tiangolo.com/"
Repository = "https://github.com/tiangolo/fastapi"

[project.optional-dependencies]

standard = [

```Python hl_lines="9-13  36-53"
{!../../../docs_src/openapi_callbacks/tutorial001.py!}
```

!!! tip
    The `callback_url` query parameter uses a Pydantic <a href="https://docs.pydantic.dev/latest/concepts/types/#urls" class="external-link" target="_blank">URL</a> type.

The only new thing is the `callbacks=invoices_callback_router.routes` as an argument to the *path operation decorator*. We'll see what that is next.

In many cases your application could need some external settings or configurations, for example secret keys, database credentials, credentials for email services, etc.

Most of these settings are variable (can change), like database URLs. And many could be sensitive, like secrets.

For this reason it's common to provide them in environment variables that are read by the application.

## Environment Variables

!!! tip

// Excerpts from @lsegal - https://github.com/aws/aws-sdk-js/issues/659#issuecomment-120477258
//
//	User-Agent:
//
//	    This is ignored from signing because signing this causes problems with generating pre-signed URLs
//	    (that are executed by other agents) or when customers pass requests through proxies, which may
//	    modify the user-agent.
//
//	Authorization:
//
//	    Is skipped for obvious reasons

# BEGIN TF REMOTE BUILD EXECUTION OPTIONS
# Options when using remote execution
# WARNING: THESE OPTIONS WONT WORK IF YOU DO NOT HAVE PROPER AUTHENTICATION AND PERMISSIONS

# Allow creation of resultstore URLs for any bazel invocation
build:resultstore --google_default_credentials
build:resultstore --bes_backend=buildeventservice.googleapis.com
build:resultstore --bes_instance_name="tensorflow-testing"

### Docs

* ✏ Tweak wording to clarify `docs/en/docs/project-generation.md`. PR [#5930](https://github.com/tiangolo/fastapi/pull/5930) by [@chandra-deb](https://github.com/chandra-deb).
* ✏ Update Pydantic GitHub URLs. PR [#5952](https://github.com/tiangolo/fastapi/pull/5952) by [@yezz123](https://github.com/yezz123).
* 📝 Add opinion from Cisco. PR [#5981](https://github.com/tiangolo/fastapi/pull/5981) by [@tiangolo](https://github.com/tiangolo).