.. _authentication-traits:

---------------------
Authentication traits
---------------------

.. smithy-trait:: smithy.api#authDefinition
.. _authDefinition-trait:


``authDefinition`` trait
========================

Summary
    A meta-trait that marks a trait as an authentication scheme. Traits
    that are marked with this trait are applied to service shapes to
    indicate how a client can authenticate with the service.
Trait selector
    ``[trait|trait]``
Value type
    An object with the following properties:

    .. list-table::
       :header-rows: 1
       :widths: 10 23 67

       * - Property
         - Type
         - Description
       * - traits
         - [:ref:`shape-id`]
         - List of shape IDs that auth scheme implementations MUST
           understand in order to successfully use the scheme. Each shape
           MUST exist and MUST be a trait. Code generators SHOULD ensure
           that they support each listed trait.

Every operation in the closure of a service is expected to support the
authentication schemes applied to a service unless the service or operation
is marked with the :ref:`auth-trait`, which is used to change the set of
supported authentication schemes.

The following example defines a service that supports both ``httpBasicAuth``
and the hypothetical ``fooExample`` authentication scheme.

.. code-block:: smithy

    $version: "2"
    namespace smithy.example

    @authDefinition
    @trait(selector: "service")
    structure fooExample {}

    @fooExample
    @httpBasicAuth
    service WeatherService {
        version: "2017-02-11"
    }

Because authentication scheme definitions are just specialized shapes, they
can also support configuration settings.

.. code-block:: smithy

    $version: "2"
    namespace smithy.example

    @authDefinition
    @trait(selector: "service")
    structure algorithmAuth {
        algorithm: AlgorithmAuthAlgorithm
    }

    @private
    enum AlgorithmAuthAlgorithm {
        SHA2 = "SHA-2"
    }

    @algorithmAuth(algorithm: "SHA-2")
    service WeatherService {
        version: "2017-02-11"
    }


.. smithy-trait:: smithy.api#httpBasicAuth
.. _httpBasicAuth-trait:

``httpBasicAuth`` trait
=======================

Summary
    Indicates that a service supports HTTP Basic Authentication as
    defined in :rfc:`2617`.
Trait selector
    ``service``
Value type
    Annotation trait.

.. code-block:: smithy

    @httpBasicAuth
    service WeatherService {
        version: "2017-02-11"
    }


.. smithy-trait:: smithy.api#httpDigestAuth
.. _httpDigestAuth-trait:

``httpDigestAuth`` trait
========================

Summary
    Indicates that a service supports HTTP Digest Authentication as defined
    in :rfc:`2617`.
Trait selector
    ``service``
Value type
    Annotation trait.

.. code-block:: smithy

    @httpDigestAuth
    service WeatherService {
        version: "2017-02-11"
    }


.. smithy-trait:: smithy.api#httpBearerAuth
.. _httpBearerAuth-trait:

``httpBearerAuth`` trait
========================

Summary
    Indicates that a service supports HTTP Bearer Authentication as defined
    in :rfc:`6750`.
Trait selector
    ``service``
Value type
    Annotation trait.

.. code-block:: smithy

    @httpBearerAuth
    service WeatherService {
        version: "2017-02-11"
    }


.. smithy-trait:: smithy.api#httpApiKeyAuth
.. _httpApiKeyAuth-trait:

``httpApiKeyAuth`` trait
========================

Summary
    Indicates that a service supports HTTP-specific authentication using an
    API key sent in a header or query string parameter.
Trait selector
    ``service``
Value type
    Object

The ``httpApiKeyAuth`` trait is an object that supports the following
properties:

.. list-table::
    :header-rows: 1
    :widths: 10 10 80

    * - Property
      - Type
      - Description
    * - name
      - ``string``
      - **Required**. Defines the name of the HTTP header or query string
        parameter that contains the API key.
    * - in
      - ``string``
      - **Required**. Defines the location of where the key is serialized.
        This value can be set to ``header`` or ``query``.
    * - scheme
      - ``string``
      - Defines the scheme to use on the ``Authorization`` header value. As
        defined in :rfc:`9110#section-11.4`. This scheme SHOULD be one of the
        schemes defined in the `IANA Authentication Scheme Registry`_. This can
        only be set if the "in" property is set to ``header``.

The following example defines a service that accepts an API key in the "X-Api-Key"
HTTP header:

.. code-block:: smithy

    @httpApiKeyAuth(name: "X-Api-Key", in: "header")
    service WeatherService {
        version: "2017-02-11"
    }

The following example defines a service that uses an API key auth scheme through
the HTTP ``Authorization`` header:

.. code-block:: smithy

    @httpApiKeyAuth(scheme: "ApiKey", name: "Authorization", in: "header")
    service WeatherService {
        version: "2017-02-11"
    }


.. smithy-trait:: smithy.api#optionalAuth
.. _optionalAuth-trait:

``optionalAuth`` trait
======================

Summary
    Indicates that an operation MAY be invoked without authentication,
    regardless of any authentication traits applied to the operation.
Trait selector
    ``operation``
Value type
    Annotation trait.

The following example defines a service that uses HTTP digest authentication,
and bound to the service is an operation that supports unauthenticated access.

.. code-block:: smithy

    @httpDigestAuth
    service WeatherService {
        version: "2017-02-11"
        operations: [PingServer]
    }

    @optionalAuth
    operation PingServer {}

The following example defines an operation that does not support
*any* authentication. This kind of operation does not require the
``optionalAuth`` trait.

.. code-block:: smithy

    @auth([])
    operation SomeUnauthenticatedOperation {}


.. smithy-trait:: smithy.api#auth
.. _auth-trait:

``auth`` trait
==============

Summary
    Defines the priority ordered authentication schemes supported by a service
    or operation. When applied to a service, it defines the default
    authentication schemes of every operation in the service. When applied
    to an operation, it defines the list of all authentication schemes
    supported by the operation, overriding any ``auth`` trait specified
    on a service.
Trait selector
    ``:is(service, operation)``

    *Service or operation shapes*
Value type
    This trait contains a priority ordered list of unique string values that
    reference authentication scheme shape IDs defined on a service
    shape.

Operations that are not annotated with the ``auth`` trait inherit the ``auth``
trait of the service they are bound to. If the operation is not annotated with
the ``auth`` trait, and the service it is bound to is also not annotated with
the ``auth`` trait, then the operation is expected to support each of the
:ref:`authentication scheme traits <authDefinition-trait>` applied to the
service. Each entry in the ``auth`` trait is a shape ID that MUST refer to an
authentication scheme trait applied to the service in which it is bound.

.. note::
    When a service has multiple authentication scheme traits applied and no
    ``auth`` trait, the ordering of authentication schemes is alphabetical
    based on the absolute shape ID of each authentication scheme trait.

The following example defines all combinations in which ``auth`` can be applied
to services and operations:

* ``ServiceWithNoAuthTrait`` does not use the ``auth`` trait and binds two
  operations:

  * ``OperationA`` is not annotated with the ``auth`` trait and inherits all
    of the authentication scheme applied to the service.

  * ``OperationB`` is annotated with the ``auth`` trait and defines an explicit
    list of authentication schemes.

* ``ServiceWithAuthTrait`` is annotated with the ``auth`` trait and binds two
  operations:

  * ``OperationC`` is not annotated with the ``auth`` trait and inherits all
    of the authentication schemes applied via the ``auth`` trait on the
    service.

  * ``OperationD`` is annotated with the ``auth`` trait and defines an explicit
    list of authentication schemes.

  * ``OperationE`` has authentication disabled by setting the ``auth`` trait
    value on the operation to an empty list, ``[]``.

.. note::
    Disabling authentication for an operation is distinct from applying the
    :ref:`@optionalAuth <optionalAuth-trait>` trait to an operation. An
    operation with the ``@optionalAuth`` trait must be callable both with and
    without authentication.

.. code-block:: smithy

    @httpBasicAuth
    @httpDigestAuth
    @httpBearerAuth
    service ServiceWithNoAuthTrait {
        version: "2020-01-29"
        operations: [
            OperationA
            OperationB
        ]
    }

    // This operation does not have the @auth trait and is bound to a service
    // without the @auth trait. The effective set of authentication schemes it
    // supports are: httpBasicAuth, httpDigestAuth and httpBearerAuth
    operation OperationA {}

    // This operation does have the @auth trait and is bound to a service
    // without the @auth trait. The effective set of authentication schemes it
    // supports are: httpDigestAuth.
    @auth([httpDigestAuth])
    operation OperationB {}

    @httpBasicAuth
    @httpDigestAuth
    @httpBearerAuth
    @auth([httpBasicAuth, httpDigestAuth])
    service ServiceWithAuthTrait {
        version: "2020-01-29"
        operations: [
            OperationC
            OperationD
            OperationE
        ]
    }

    // This operation does not have the @auth trait and is bound to a service
    // with the @auth trait. The effective set of authentication schemes it
    // supports are: httpBasicAuth, httpDigestAuth
    operation OperationC {}

    // This operation has the @auth trait and is bound to a service
    // with the @auth trait. The effective set of authentication schemes it
    // supports are: httpBearerAuth
    @auth([httpBearerAuth])
    operation OperationD {}

    // This operation has the @auth trait and is bound to a service with the
    // @auth trait. This operation does not support any authentication schemes.
    @auth([])
    operation OperationE {}

The following ``auth`` trait is invalid because it references an
authentication scheme trait that is not applied to the service:

.. code-block:: smithy

    @httpDigestAuth
    @auth([httpBasicAuth]) // <-- Invalid!
    service InvalidExample {
        version: "2017-02-11"
    }

The following operation ``auth`` trait is invalid because it references an
authentication scheme trait that is not applied to the service:

.. code-block:: smithy

    @httpDigestAuth
    service InvalidExample {
        version: "2017-02-11",
        operations: [OperationA]
    }

    @auth([httpBasicAuth]) // <-- Invalid!
    operation OperationA {}


.. _IANA Authentication Scheme Registry: https://www.iana.org/assignments/http-authschemes