# Sub Applications - Mounts { #sub-applications-mounts }

If you need to have two independent FastAPI applications, with their own independent OpenAPI and their own docs UIs, you can have a main app and "mount" one (or more) sub-application(s).

## Mounting a **FastAPI** application { #mounting-a-fastapi-application }

# Exceptions - `HTTPException` and `WebSocketException`

These are the exceptions that you can raise to show errors to the client.

When you raise an exception, as would happen with normal Python, the rest of the execution is aborted. This way you can raise these exceptions from anywhere in the code to abort a request and show the error to the client.

You can use:

* `HTTPException`
* `WebSocketException`

    attributes:
      label: "What did you see happen?"
    validations:
      required: true
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    id: expected-behavior
    attributes:
      label: "What did you expect to see?"
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    id: editor-and-settings
    attributes:
      label: "Editor and settings"

  - type: textarea
    attributes:
      label: API(s)
      description: Which existing classes or methods do you want to improve?
      placeholder: e.g., `com.google.common.collect.ImmutableList::of`
      render: java
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      required: true

  - type: textarea
    attributes:
      label: How do you want it to be improved?
    validations:
      required: true

  - type: textarea
    attributes:

management](https://github.com/minio/minio/blob/master/docs/bucket/lifecycle/README.md).  If you have an object expiration lifecycle policy in your non-versioned bucket and you want to maintain the same permanent delete behavior when on versioning-enabled bucket, you must add a noncurrent expiration policy. The noncurrent expiration lifecycle policy will manage the deletes of the noncurrent object versions in the versioning-enabled bucket. (A version-enabled bucket maintains one current and zero or more...

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## Context
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## Use `CORSMiddleware` { #use-corsmiddleware }

You can configure it in your **FastAPI** application using the `CORSMiddleware`.

* Import `CORSMiddleware`.
* Create a list of allowed origins (as strings).
* Add it as a "middleware" to your **FastAPI** application.

You can also specify whether your backend allows:

* Credentials (Authorization headers, Cookies, etc).

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

Contributing
============

If you would like to contribute code to OkHttp you can do so through GitHub by
forking the repository and sending a pull request.

When submitting code, please make every effort to follow existing conventions
and style in order to keep the code as readable as possible. Please also make
sure your code compiles by running `./gradlew check`. Checkstyle failures
during compilation indicate errors in your style and can be viewed in the

                    description="""
                                ChimichangApp API helps you do awesome stuff. 🚀

                                ## Items

                                You can **read items**.

                                ## Users

                                You will be able to:

                                * **Create users** (_not implemented_).