.. index:: single: jwt_jwa
.. _jwt_jwa/0:

.. rst-class:: right

**object**

``jwt_jwa``
===========

JSON Web Algorithm metadata and header helpers.

| **Availability:** 
|    ``logtalk_load(jwt(loader))``

| **Author:** Paulo Moura
| **Version:** 1:0:0
| **Date:** 2026-07-06

| **Compilation flags:**
|    ``static, context_switching_calls``


| **Imports:**
|    ``public`` :ref:`jwt_helpers <jwt_helpers/0>`
| **Uses:**
|    :ref:`list <list/0>`

| **Remarks:**
|    (none)

| **Inherited public predicates:**
|     :ref:`options_protocol/0::check_option/1`  :ref:`options_protocol/0::check_options/1`  :ref:`options_protocol/0::default_option/1`  :ref:`options_protocol/0::default_options/1`  :ref:`options_protocol/0::option/2`  :ref:`options_protocol/0::option/3`  :ref:`options_protocol/0::valid_option/1`  :ref:`options_protocol/0::valid_options/1`  

.. contents::
   :local:
   :backlinks: top

Public predicates
-----------------

.. index:: header_algorithm/2
.. _jwt_jwa/0::header_algorithm/2:

``header_algorithm/2``
^^^^^^^^^^^^^^^^^^^^^^

Extracts and validates the JWT header algorithm.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``header_algorithm(Header,Algorithm)``
| **Mode and number of proofs:**
|    ``header_algorithm(+term,-atom)`` - ``one_or_error``

| **Exceptions:**
|    ``Header`` does not contain a valid ``alg`` member:
|        ``domain_error(jwt_header,Header)``


------------

.. index:: header_key_id/2
.. _jwt_jwa/0::header_key_id/2:

``header_key_id/2``
^^^^^^^^^^^^^^^^^^^

Extracts the optional key identifier from a JWT header.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``header_key_id(Header,KeyId)``
| **Mode and number of proofs:**
|    ``header_key_id(+term,-atom)`` - ``zero_or_one``


------------

.. index:: validate_header/1
.. _jwt_jwa/0::validate_header/1:

``validate_header/1``
^^^^^^^^^^^^^^^^^^^^^

Validates a JWT header object and rejects unsupported critical header parameters.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``validate_header(Header)``
| **Mode and number of proofs:**
|    ``validate_header(+term)`` - ``one_or_error``

| **Exceptions:**
|    ``Header`` is not a JSON object, contains duplicate member names, or contains unsupported critical header parameters:
|        ``domain_error(jwt_header,Header)``


------------

.. index:: allowed_algorithm/2
.. _jwt_jwa/0::allowed_algorithm/2:

``allowed_algorithm/2``
^^^^^^^^^^^^^^^^^^^^^^^

Validates that an algorithm is supported and allowed by the options.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``allowed_algorithm(Algorithm,Options)``
| **Mode and number of proofs:**
|    ``allowed_algorithm(+atom,+list(compound))`` - ``one_or_error``

| **Exceptions:**
|    ``Algorithm`` is unsupported or disallowed by ``Options``:
|        ``domain_error(jwt_algorithm,Algorithm)``


------------

.. index:: supported_algorithm/1
.. _jwt_jwa/0::supported_algorithm/1:

``supported_algorithm/1``
^^^^^^^^^^^^^^^^^^^^^^^^^

Succeeds when the algorithm is supported by this library.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``supported_algorithm(Algorithm)``
| **Mode and number of proofs:**
|    ``supported_algorithm(+atom)`` - ``zero_or_one``


------------

.. index:: key_type/2
.. _jwt_jwa/0::key_type/2:

``key_type/2``
^^^^^^^^^^^^^^

Maps a supported algorithm to the required JWK key type.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``key_type(Algorithm,KeyType)``
| **Mode and number of proofs:**
|    ``key_type(+atom,-atom)`` - ``zero_or_one``


------------

.. index:: hmac_hash/2
.. _jwt_jwa/0::hmac_hash/2:

``hmac_hash/2``
^^^^^^^^^^^^^^^

Maps a supported HMAC algorithm to its hash object.

| **Compilation flags:**
|    ``static``

| **Template:**
|    ``hmac_hash(Algorithm,Hash)``
| **Mode and number of proofs:**
|    ``hmac_hash(+atom,-object_identifier)`` - ``zero_or_one``


------------

Protected predicates
--------------------

(no local declarations; see entity ancestors if any)

Private predicates
------------------

(no local declarations; see entity ancestors if any)

Operators
---------

(none)