.. This file is part of GNU TALER. Copyright (C) 2023 Taler Systems SA TALER is free software; you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation; either version 2.1, or (at your option) any later version. TALER is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details. You should have received a copy of the GNU Affero General Public License along with TALER; see the file COPYING. If not, see @author Christian Grothoff .. _challenger-api: ====================== Challenger Service API ====================== The challenger service validates that a user is able to receive challenges at an address (such as e-mail or SMS) and allows an OAuth 2.0 client to obtain access to these validated addresses. The high-level flow is that an OAuth 2.0 client is first registered with the challenger service (via command-line). Using the command-line tool will print the resulting client ID to the console. .. note:: The current service mandates that redirection URIs start with "http://" or "https://". See issue #7838 for what should be done to lift this restriction. .. note:: Right now, registration of a unique redirection URI is *mandatory* for each client. If multiple redirection URIs are needed, it is suggested to just register additional clients. (While OAuth 2.0 would support not registering fixed redirection URIs with a client, this is not recommended as it would create an open redirector.) Once a client is registered, that client can use the challenger service when it needs a user to prove that the user is able to receive messages at a particular address. However, asking a user to prove access to a particular address can be expensive as it may involve sending an SMS or even postal mail depending on the type of address. Thus, challenger does not allow a user agent to begin an address validation process without prior approval by a registered client. Thus, the process begins with a ``/setup/$CLIENT_ID`` request where a client requests challenger to begin an address validation request. The ``/setup/$CLIENT_ID`` response contains a ``nonce`` which is then used to construct the URL of the endpoint to which the client must redirect the user-agent to begin the address validation and authorization process. The client then redirects the user-agent to the ``/authorize/$NONCE`` endpoint of the challenger service, adding its ``state``, ``client_id`` and ``redirect_uri`` as query parameters. The ``redirect_uri`` must match the redirect URI registered with the client. From this endpoint, the challenger service will return a Web page asking the user to provide its address. .. note:: Challenger is a bit unusual in that the ``$NONCE`` in the endpoint URL makes the authorization endpoint URL (deliberately) unpredictable, while for many other OAuth 2.0 APIs this endpoint is static. However, this is compliant with OAuth 2.0 as determining the authorization URL is left out of the scope of the standard. When the user has filled in the form with their address, it will be submitted to the ``/challenge/$NONCE`` endpoint and the challenger service will send a challenge to the user's address and generate an HTML form asking the user to enter the received challenge value. The user can then enter the answer to the challenge which is then submitted to the ``/solve/$NONCE`` endpoint. If the answer is correct, the user agent will be redirected to the client redirect URI that was specified by the OAuth 2.0 client upon ``/authorize``, together with an authorization grant encoded in the redirection URI. Given this authorization grant, the OAuth 2.0 client can then use the ``/token`` endpoint to obtain an access token which will grant it access to the resource. Using the ``/info`` endpoint the client can then finally obtain the (now) verified address of the user. .. contents:: Table of Contents :local: .. include:: tos.rst ----------------------- Receiving Configuration ----------------------- .. http:get:: /config Obtain the key configuration settings of the storage service. This specification corresponds to ``current`` protocol being version **0**. **Response:** Returns a `ChallengerTermsOfServiceResponse`. .. ts:def:: ChallengerTermsOfServiceResponse interface ChallengerTermsOfServiceResponse { // Name of the service name: "challenger"; // libtool-style representation of the Challenger protocol version, see // https://www.gnu.org/software/libtool/manual/html_node/Versioning.html#Versioning // The format is "current:revision:age". version: string; // URN of the implementation (needed to interpret 'revision' in version). // @since v0, may become mandatory in the future. implementation?: string; } .. _challenger-setup: ----- Setup ----- .. http:post:: /setup/$CLIENT_ID This endpoint is used by the client to authorize the execution of an address validation on its behalf. An ``Authorization`` header (for now always using a ``Bearer`` token) should be included to provide the client's credentials to authorize access to the challenger service. This token must match the ``client_secret`` from the registration of the client with the challenger service (which will also be used in the later ``/token`` request). **Response:** :http:statuscode:`200 OK`: Response is a `ChallengeSetupResponse`. :http:statuscode:`404 Not found`: The backup service is unaware of a matching client. or the credentials of the client are invalid. **Details::** .. ts:def:: ChallengeSetupResponse interface ChallengeSetupResponse { // Nonce to use when constructing ``/authorize`` endpoint. nonce: string; } .. _challenger-login: ----- Login ----- .. http:get:: /authorize/$NONCE .. http:post:: /authorize/$NONCE This is the "authorization" endpoint of the OAuth 2.0 protocol. This endpoint is used by the user-agent. It will return a form to enter the address. **Request:** :query response_type: Must be ``code`` :query client_id: Identifier of the client. :query redirect_uri: URI-encoded redirection URI to use upon authorization. :query state: Arbitrary client state to associate with the request. :query scope: Not supported, any value is accepted. **Response:** :http:statuscode:`200 OK`: The body contains a form to be submitted by the user-agent. The form will ask the user to specify their address. :http:statuscode:`404 Not found`: The backup service is unaware of a matching $NONCE. .. _challenger-challenge: --------- Challenge --------- .. http:post:: /challenge/$NONCE This endpoint is used by the user-agent to submit the address to which a challenge should be sent by the challenger service. **Request:** Body should use the mime-type "application/x-www-form-urlencoded". The posted form data must contain an "address". **Response:** :http:statuscode:`200 OK`: The body contains a form asking for the answer to the challenge to be entered by the user. :http:statuscode:`404 Not found`: The challenger service is unaware of a matching nonce. :http:statuscode:`429 Too Many Requests`: There have been too many attempts to request challenge transmissions for this $NONCE. The user-agent should wait and (eventually) request a fresh nonce to be set up by the client. .. _challenger-solve: ----- Solve ----- .. http:post:: /solve/$NONCE Used by the user-agent to submit an answer to the challenge. If the answer is correct, the user will be redirected to the client's redirect URI, otherwise the user may be given another chance to complete the process. **Request:** Depends on the form from ``/challenge``. TBD. **Response:** :http:statuscode:`302 Found`: The user is redirected to the redirect URI of the client to pass the grant to the client. The target will be the redirect URI specified by the client (during registration and again upon ``/authorize``), plus a ``code`` argument with the authorization code, and the ``state`` argument from the ``/authorize`` endpoint. :http:statuscode:`403 Forbidden`: The solution of the user to the challenge is invalid. :http:statuscode:`404 Not found`: The service is unaware of a matching challenge. :http:statuscode:`429 Too Many Requests`: There have been too many attempts to solve the challenge for this address (and $NONCE). The user-agent should either try a different address (or wait and (eventually) request a fresh nonce to be set up by the client). .. _challenger-auth: ---- Auth ---- .. http:post:: /token This is the token endpoint of the OAuth 2.0 specification. This endpoint is used by the client to provide its authorization code, demonstrating that it has the right to learn a particular user's validated address. In return, the challenger service returns the access token. Renewal is not supported. **Request:** The request must include an ``application/www-form-urlencoded`` body specifying the ``client_id``, ``redirect_uri``, ``client_secret``, ``code`` and ``grant_type``. The ``grant_type`` must be set to ``authorization_code``. The ``redirect_uri`` must match the URI from ``/authorize``. The ``code`` must be the authorization code that ``/solve`` returned to the user. The ``client_id`` and ``client_secret`` must match the usual client credentials. **Response:** Error responses follow RFC 6749, section 5.2 with an "error" field in JSON, as well as also returning GNU Taler style error messages. :http:statuscode:`200 OK`: The body will be a `ChallengerAuthResponse` :http:statuscode:`403 Forbidden`: The credentials of the client are invalid. :http:statuscode:`404 Not found`: The service is unaware of a matching login process. **Details::** .. ts:def:: ChallengerAuthResponse interface ChallengerAuthResponse { // Token used to authenticate access in ``/info``. access_token: string; // Type of the access token. token_type: "Bearer"; // Amount of time that an access token is valid (in seconds). expires_in: Integer; } .. _challenger-info: ---- Info ---- .. http:get:: /info This userinfo endpoint of the OAuth 2.0 specification. This endpoint is used by the client to obtain the user's validated address. **Request:** Must include the token returned to the client from the ``/token`` endpoint as a ``Bearer`` token in an ``Authorization`` header. **Response:** :http:statuscode:`200 OK`: The body contains the address as a `ChallengerInfoResponse`. :http:statuscode:`403 Forbidden`: The bearer token is missing or invalid (malformed). :http:statuscode:`404 Not found`: The bearer token is invalid (includes unknown or expired). **Details::** .. ts:def:: ChallengerInfoResponse interface ChallengerInfoResponse { // Unique ID of the record within Challenger // (identifies the rowid of the token). id: Integer; // Address that was validated. // Key-value pairs, details depend on the // address_type. address: Object; // Type of the address. address_type: string; // How long do we consider the address to be // valid for this user. expires: Timestamp; }