# User Application

Tryton provides a way to connect URL rules to an callable endpoint using the decorator method route of the trytond.application.app instance. This allows to define a custom API based on HTTP that can be used to create a specific user application.

The decorator takes as first parameter a string which follow the Rule Format of Werkzeug and as second parameter sequence of HTTP methods.

Example:

    from trytond.application import app

    @app.route('/hello', methods=['GET'])
    def hello(request):
        return 'Hello world'

Tryton also provides some wrappers in trytond.protocols.wrappers to ease the creation of such route.

> - set_max_request_size(size): change the default limit of the request to the size in bytes.
> - with_pool: which takes the first parameter as database name and replace it by the corresponding instance of the Pool.
> - with_transaction([readonly]): which starts a `Transaction` using the Pool from with_pool. If readonly is not set, the transaction will not be readonly for POST, PUT, DELETE and PATCH methods and readonly for all others.
> - user_application(name[, json]): which set the `Transaction.user` from the Authorization header using the type bearer and a valid key for the named user application.

## User Application Key

Tryton also provides a easy way to manage access to user application using keys per named application. A key is created with a POST request on the URL /<database_name>/user/application/ which returns the key. The request must contain as data a json object with the keys:

> - user: the user login
> - application: the name of the application

After the creation, the key must be validated by the user from the preferences of a Tryton client.

A key can be deleted with a DELETE request on the same URL. The request must contain as data a json object with the keys:

> - user: the user login
> - key: the key to delete
> - application: the name of the application of the key