..
  This file is part of GNU TALER.
  Copyright (C) 2014-2023 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 <http://www.gnu.org/licenses/>

  @author Christian Grothoff
  @author Pius Loosli
  @author Lukas Matyja
  @author Johannes Casaburi

.. _donau-api:

=====================
The Donau RESTful API
=====================

The API specified here follows the :ref:`general conventions <http-common>`
for all details not specified in the individual requests.
The `glossary <https://docs.taler.net/taler-developer-manual.html#developer-glossary>`_
defines all specific terms used in this section.

.. contents:: Table of Contents
  :local:

.. _donau-overview:

------------
API Overview
------------

This is intended to provide a quick overview of the whole REST API. For a more detailed view of the protocol, see the protocol specification.

The chapters group the families of requests frequently encountered when using the Donau API:

* :ref:`Status information<donau_status>`: get the public signing keys of the Donau, the donation unit key, the Donaus config or some entropy
* :ref:`Issue receipts<donau_issue>`: For use by charities: Issue receipts with blinded unique donor ids from a donor.
* :ref:`Donation statement<donation_statement>`: Summarizes the donation receipts to the donation statement signature which is made over the total yearly donation amount,
          the year and the hash of taxid+salt. Provides an API to get the donation statement signature.
* :ref:`Charity administration and status information<donau_charity>`:

  * For use by administrators to add/modify a charity
  * For use by charities to get their remaining donation volume

.. include:: tos.rst

.. _donau_status:

----------------------------------------
Donau public keys and status information
----------------------------------------

This API is used by donors and charities to obtain global information about
the Donau, such as online signing keys and available donation units.  This is
typically the first call any Donau client makes, as it returns information
required to process all of the other interactions with the Donau.  The
returned information is secured by signature(s) from the Donau, especially the
long-term offline signing key of the Donau, which clients should cache.

.. http:get:: /keys

  Get a list of all donation units keys offered by the Donau,
  as well as the Donau's current online signing key (used for donation statements).

  **Request:**

  **Response:**

  :http:statuscode:`200 OK`:
    The Donau responds with a `DonauKeysResponse` object. This request should
    virtually always be successful. It only fails if the Donau is misconfigured.

  **Details:**

  .. ts:def:: DonauKeysResponse

    interface DonauKeysResponse {
      // libtool-style representation of the Donau protocol version, see
      // https://www.gnu.org/software/libtool/manual/html_node/Versioning.html#Versioning
      // The format is "current:revision:age".
      version: string;

      // Financial domain this Donau operates for.
      domain: string;

      // The Donau's base URL.
      base_url: string;

      // The Donau's currency.
      currency: string;

      // How many digits should the amounts be rendered
      // with by default. Small capitals should
      // be used to render fractions beyond the number
      // given here (like on gas stations).
      currency_fraction_digits: Integer;

      // Donation Units offered by this Donau
      donation_units: DonationUnitKeyGroup[];

      // The Donau's signing keys.
      signkeys: SignKey[];

    }

  .. ts:def:: DonationUnitKeyGroup

    type DonationUnitKeyGroup =
      | DonationUnitKeyGroupRsa
      | DonationUnitKeyGroupCs;

  .. ts:def:: DonationUnitKeyGroupRsa

    interface DonationUnitKeyGroupRsa extends DonationUnitKeyGroupCommon {
      cipher: "RSA";

      donation_units: ({
        rsa_pub: RsaPublicKey;
      } & DonationUnitKeyCommon)[];
    }

  .. ts:def:: DonationUnitKeyGroupCs

    interface DonationUnitKeyGroupCs extends DonationUnitKeyGroupCommon {
      cipher: "CS";

      donation_units: ({
        cs_pub: Cs25519Point;
      } & DonationUnitKeyCommon)[];
    }

  .. ts:def:: DonationUnitKeyGroupCommon

    // Common attributes for all donation unit groups
    interface DonationUnitKeyGroupCommon {
      // How much was donated based on this donation receipt.
      value: Amount;

    }

  .. ts:def:: DonationUnitKeyCommon

    interface DonationUnitKeyCommon {

      // For which year is this donation unit key valid.
      year: Integer;

      // Set to 'true' if the Donau somehow "lost" the private key. The donation unit was not
      // revoked, but still cannot be used to withdraw receipts at this time (theoretically,
      // the private key could be recovered in the future; receipts signed with the private key
      // remain valid).
      lost?: boolean;
    }

  .. ts:def:: DonationUnitKey

    type DonationUnitKey =
      | RsaDonationUnitKey
      | CSDonationUnitKey;

  .. ts:def:: RsaDonationUnitKey

    interface RsaDonationUnitKey {
      cipher: "RSA";

      // RSA public key
      rsa_public_key: RsaPublicKey;
    }

  .. ts:def:: CSDonationUnitKey

    interface CSDonationUnitKey {
      cipher: "CS";

      // Public key of the donation unit.
      cs_public_key: Cs25519Point;

    }

  A signing key in the ``signkeys`` list is a JSON object with the following fields:

  .. ts:def:: SignKey

    interface SignKey {
      // The actual Donau's EdDSA signing public key.
      key: EddsaPublicKey;

      // Initial validity date for the signing key.
      year: Integer;

    }


  .. note::

    Both the individual donation units *and* the donation units list is signed,
    allowing customers to prove that they received an inconsistent list.

.. http:get:: /seed

  Return an entropy seed. The Donau will return a high-entropy
  value that will differ for every call.  The response is NOT in
  JSON, but simply high-entropy binary data in the HTTP body.
  This API should be used by wallets to guard themselves against
  running on low-entropy (bad PRNG) hardware. Naturally, the entropy
  returned MUST be mixed with locally generated entropy.

.. http:get:: /config

  Return the protocol version, financial domain and currency supported by this
  Donau backend.

  **Response:**

  :http:statuscode:`200 OK`:
    The body is a `DonauVersionResponse`.

  .. ts:def:: DonauVersionResponse

    interface DonauVersionResponse {
      // libtool-style representation of the Donau protocol version, see
      // https://www.gnu.org/software/libtool/manual/html_node/Versioning.html#Versioning
      // The format is "current:revision:age".
      version: string;

      // Name of the protocol.
      name: "taler-donau";

      // Currency supported by this Donau.
      currency: string;

      // Financial domain by this Donau.
      domain: string;

    }


.. _donau_issue:

--------------
Issue receipts
--------------

Inspired by the Taler exchange :ref:`Withdrawal<exchange-withdrawal>`.

This API is used to obtain valid, attested donation receipts from the Donau.
Use the :ref:`charity GET route<donau_charity_get>` to see the remaining donation volume for the current year.

CSR  Issue
~~~~~~~~~~~

.. http:post:: /csr-issue

  Obtain donau-side input values in preparation for a
  issue receipt step for certain donation unit cipher types,
  specifically at this point for Clause-Schnorr blind
  signatures. This API is used by the donor.

  **Request:** The request body must be a `IssuePrepareRequest` object.

  **Response:**

  :http:statuscode:`200 OK`:
    The request was successful, and the response is a `IssuePrepareResponse`.  Note that repeating exactly the same request
    will again yield the same response (assuming none of the donation unit is expired).
  :http:statuscode:`404 Not found`:
    The donation unit key is not known to the donau.
  :http:statuscode:`410 Gone`:
    The requested donation unit key is not yet or no longer valid. It either before the validity year, past the
    year or was revoked. The response is a `DonationUnitExpiredMessage`. Clients must evaluate the error code provided to
    understand which of the cases this is and handle it accordingly.

  **Details:**

  .. ts:def:: IssuePrepareRequest

    interface IssuePrepareRequest {

      // Nonce to be used by the donau to derive
      // its private inputs from. Must not have ever
      // been used before.
      nonce: CSNonce;

      // Hash of the public key of the donation unit
      // the request relates to.
      donation_unit_pub_hash: HashCode;

    }

  .. ts:def:: IssuePrepareResponse

    type IssuePrepareResponse =
      | DonauIssueValue;

  .. ts:def:: DonauIssueValue

    type DonauIssueValue =
      | DonauRsaIssueValue
      | DonauCsIssueValue;

  .. ts:def:: DonauRsaIssueValue

    interface DonauRsaIssueValue {
      cipher: "RSA";
    }

  .. ts:def:: DonauCsIssueValue

    interface DonauCsIssueValue {
      cipher: "CS";

      // CSR R0 value
      r_pub_0: CsRPublic;

      // CSR R1 value
      r_pub_1: CsRPublic;
    }


Batch Issue
~~~~~~~~~~~
This is the effectiv issue receipts request. Depending on the amount of the donation a
certain amount of blinded unique donation identifiers, or for short BUDIs, are required.
Every BUDI will be signed by the corresponding requested donation unit, which is associated with a value.
This API is used by the charity but the `BUDIKeyPairs` are coming from the donor.

To make the request idempotent, the hash of the hole request is recorded under the
corresponding charity_id by the Donau.

.. http:POST:: /batch-issue/$CHARITY_ID

  Send in a `IssueReceiptsRequest` and ask the Donau to sign all it's contained BUDIs.

  **Request:** `IssueReceiptsRequest`

  **Response:**

  :http:statuscode:`200 OK`:
    The request was successful, and the response is a `BlindedDonationReceiptSignatures`.
  :http:statuscode:`403 Forbidden`:
    The charity signature is invalid. This response comes with a standard `ErrorDetail` response.
  :http:statuscode:`404 Not found`:
    At least one of the donation unit keys is not known to the Donau. Comes with a `DonationUnitUnknownError`.
    This suggests a bug in the donor as it should have used current donation unit keys from :ref:`/keys<donau_status>`.
  :http:statuscode:`409 Conflict`:
    The donation volume of the charity is not sufficient to issue donation receipts for all sent in blinded udis.
    The response is a `IssueError` object.
  :http:statuscode:`410 Gone`:
    The requested donation unit key is not yet or no longer valid. It either before the validity year, past the
    year or was revoked. The response is a `DonationUnitExpiredMessage`. Clients must evaluate the error code
    provided to understand which of the cases this is and handle it accordingly.

  **Details:**

  .. ts:def:: IssueReceiptsRequest

    interface IssueReceiptsRequest {
      charity_sig: EddsaSignature;
      year: Integer;
      budikeypairs: BUDIKeyPairs[];
    }

  .. ts:def:: BUDIKeyPairs

    interface BUDIKeyPairs {
      h_donation_unit_pub: HashCode;
      blinded_udi: BUDI;
    }

  .. ts:def:: BUDI

    type BUDI = RSABUDI | CSBUDI ;

  .. ts:def:: RSABUDI

    interface RSABUDI {
      cipher: "RSA";
      rsa_blinded_udi: string;          // Crockford Base32 encoded
    }

  .. ts:def:: CSBUDI

    // For donation unit signatures based on Blind Clause-Schnorr, the BUDI
    // consists of the public nonce and two Curve25519 scalars which are two
    // blinded challenges in the Blinded Clause-Schnorr signature scheme.
    // See https://taler.net/papers/cs-thesis.pdf for details.
    interface CSBUDI {
      cipher: "CS";
      cs_nonce: string;      // Crockford Base32 encoded
      cs_blinded_c0: string; // Crockford Base32 encoded
      cs_blinded_c1: string; // Crockford Base32 encoded
    }

  .. ts:def:: BUDIBlindingKeyP

    // Secret for blinding/unblinding.
    // An RSA blinding secret, which is basically
    // a 256-bit nonce, converted to Crockford Base32.
    type BUDIBlindingKeyP = string;

  .. ts:def:: BlindedDonationReceiptSignatures

    interface BlindedDonationReceiptSignatures {
      blind_signed_receipt_signatures: BlindedDonationReceiptSignature[];
    }

  .. ts:def:: BlindedDonationReceiptSignature

    type BlindedDonationReceiptSignature =
      | RSABlindedDonationReceiptSignature
      | CSBlindedDonationReceiptSignature;

  .. ts:def:: RSABlindedDonationReceiptSignature

    interface RSABlindedDonationReceiptSignature {
      cipher: "RSA";

      // (blinded) RSA signature
      blinded_rsa_signature: BlindedRsaSignature;
    }

  .. ts:def:: CSBlindedDonationReceiptSignature

    interface CSBlindedDonationReceiptSignature {
      type: "CS";

      // Signer chosen bit value, 0 or 1, used
      // in Clause Blind Schnorr to make the
      // ROS problem harder.
      b: Integer;

      // Blinded scalar calculated from c_b.
      s: Cs25519Scalar;
    }

  .. ts:def:: IssueError

    interface IssueError{
      max_per_year: Amount;
      current_year: Amount;
    }

  .. ts:def:: DonationUnitUnknownError

    interface DonationUnitUnknownError{
      unknown_hash_pub_donation_unit: HashCode[];
      donau_pub: EddsaPublicKey;
      donau_sig: EddsaSignature;
    }

  .. ts:def:: DonationUnitExpiredMessage

    interface DonationUnitExpiredMessage{
      h_donation_unit_pub: HashCode;
      donau_pub: EddsaPublicKey;
      donau_sig: EddsaSignature;
    }

.. _donation_statement:

------------------
Donation statement
------------------

Inspired by the Taler exchange :ref:`Deposit<deposit-par>`.

Donation statement operations are requested by a donor.

.. http:POST:: /batch-submit

  Send in donation receipts for the current or one of the past fiscal years.
  The donor will reveive the signed total back, which is called the
  donation statement.

  **Request:** `SubmitDonationReceiptsRequest`

  **Response:**

  :http:statuscode:`201 Created`:
    The request was successful, and the created `DonationStatement` is stored.
  :http:statuscode:`403 Forbidden`:
    One of the signatures is invalid. This response comes with a standard `ErrorDetail` response.
  :http:statuscode:`404 Not found`:
    At least one of the donation unit keys is not known to the Donau. Comes with a `DonationUnitUnknownError`.

  **Details:**

  .. ts:def:: SubmitDonationReceiptsRequest

    interface SubmitDonationReceiptsRequest{
      // hashed taxpayer ID plus salt
      h_donor_tax_id: HashCode;
      // All donation receipts must be for this year.
      donation_year: Integer;
      // Receipts should be sorted by amount.
      donation_receipts: DonationReceipt[];
    }

  .. ts:def:: DonationReceipt

    interface DonationReceipt{
      h_donation_unit_pub: HashCode;
      nonce: string;
      donation_unit_sig: DonationReceiptSignature
    }

  .. ts:def:: DonationReceiptSignature

    type DonationReceiptSignature = RSADonationReceiptSignature | CSDonationReceiptSignature ;

  .. ts:def:: RSADonationReceiptSignature

    interface RSADonationReceiptSignature {
      cipher: "RSA";

      // RSA signature
      rsa_signature: RsaSignature;
    }

  .. ts:def:: CSDonationReceiptSignature

    interface CSDonationReceiptSignature {
      type: "CS";

      // R value component of the signature.
      cs_signature_r: Cs25519Point;

      // s value component of the signature.
      cs_signature_s: Cs25519Scalar;
    }

.. http:GET:: /donation-statement/$YEAR/$HASH_DONOR_ID

  Get the donation statement for a specific year and donor.

  **Request:**

  **Response:**

  :http:statuscode:`200 OK`:
    The request was successful, and the response is a `DonationStatementResponse`.
  :http:statuscode:`403 Forbidden`:
    One of the signatures is invalid. This response comes with a standard `ErrorDetail` response.
  :http:statuscode:`404 Not found`:
    Either the donor or the year or the corresponding donation statement was not found.
    This response comes with a standard `ErrorDetail` response.

  **Details:**

  .. ts:def:: DonationStatementResponse

    interface DonationStatementResponse {
      total: Amount;
      // signature over h_donor_tax_id, total, donation_year
      donation_statement_sig: EddsaSignature;
      // the corresponding public key to the signature
      donau_pub: EddsaPublicKey;
    }

.. _donau_charity:

---------------------------------------------
Charity administration and status information
---------------------------------------------

The administration requests require an authorized bearer token to be set in the HTTP "Authorization" Header. This token can be set by a proxy validating authentication/authorization (using e.g. LDAP).
The GET status requests require an authorized bearer token as well.

.. http:GET::  /charities

  GET all charities. Only allowed if the request comes with the administration bearer token.

  return all charities

  **Request:**

  **Reponse:**

  :http:statuscode:`200 OK`:
    The request was successful, and the response is a `Charities`.

  **Details:**

  .. ts:def:: Charities

    interface Charities{
      charities: CharitySummary[];
    }

  .. ts:def:: CharitySummary

    interface CharitySummary{
      charity_id: Integer;
      name: string;
      max_per_year: Amount;
      receipts_to_date: Amount;
    }

.. _donau_charity_get:

.. http:get:: /charities/$CHARITY_ID

  GET a specific charity. Only allowed if the request comes with the charity or administration bearer token.

  Request information about a charity.

  **Request:**

  **Response:**

  :http:statuscode:`200 OK`:
    The Donau responds with a `Charity` object
  :http:statuscode:`404 Not found`:
    The charity id does not belong to a charity known to the Donau.

  .. ts:def:: Charity

    interface Charity {
      charity_pub: EddsaPublicKey;
      name: string;
      url: string;
      max_per_year: Amount;
      receipts_to_date: Amount;
      current_year: Integer;
    }

.. http:POST:: /charity

  Add a charity. Only allowed if the request comes with the administrator bearer token.

  **Request:** `CharityRequest`

  **Response:**

  **Details:**

  :http:statuscode:`201 Created`:
    The request was successful, and the response is a `CharityResponse`.

  :http:statuscode:`403 Forbidden`:
    The request did not contain an accepted administrator bearer token in it's header.

  .. ts:def:: CharityRequest

    interface CharityRequest{
      charity_pub: EddsaPublicKey;
      name: string;
      url: string;
      max_per_year: Amount;
      receipts_to_date: Amount;
      current_year: Integer;
    }

  .. ts:def:: CharityResponse

    interface CharityResponse{
      id: Integer;
    }


.. http:PATCH:: /charities/{id}

  Modify a charity. Only allowed if the request comes with the administrator bearer token.

  **Request:** `CharityRequest`

  **Response:**

  :http:statuscode:`200 OK`:
    The request was successful.

  :http:statuscode:`403 Forbidden`:
    The request did not contain an accepted administrator bearer token in it's header.


.. http:DELETE:: /charities/{id}

  Delete (or deactivate) a charity. Only allowed if the request comes with the administrator bearer token.

  **Request:**

  **Response:**

  :http:statuscode:`204 No content`:
    The request was successful.

  :http:statuscode:`403 Forbidden`:
    The request did not contain an accepted administrator bearer token in it's header.