From 0a26124e12df5436641d6ad6e8586635a74293a8 Mon Sep 17 00:00:00 2001 From: Florian Dold Date: Thu, 29 Aug 2019 13:46:43 +0200 Subject: missing files --- taler-merchant-api-tutorial.rst | 1703 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 1703 insertions(+) create mode 100644 taler-merchant-api-tutorial.rst (limited to 'taler-merchant-api-tutorial.rst') diff --git a/taler-merchant-api-tutorial.rst b/taler-merchant-api-tutorial.rst new file mode 100644 index 00000000..cc4ede93 --- /dev/null +++ b/taler-merchant-api-tutorial.rst @@ -0,0 +1,1703 @@ +The GNU Taler Merchant API Tutorial +################################### + +Introduction +============ + +About GNU Taler +--------------- + +GNU Taler is an open protocol for an electronic payment system with a +free software reference implementation. GNU Taler offers secure, fast +and easy payment processing using well understood cryptographic +techniques. GNU Taler allows customers to remain anonymous, while +ensuring that merchants can be held accountable by governments. Hence, +GNU Taler is compatible with anti-money-laundering (AML) and +know-your-customer (KYC) regulation, as well as data protection +regulation (such as GDPR). + +About this tutorial +------------------- + +This tutorial addresses how to process payments using the GNU Taler +merchant Backend. This chapter explains some basic concepts. In the +second chapter, you will learn how to do basic payments. + +This version of the tutorial has examples for Python3. It uses the +requests library for HTTP requests. Versions for other +languages/environments are available as well. + +examples +git +If you want to look at some simple, running examples, check out these: + +- The `essay + merchant `__ + that sells single chapters of a book. + +- The `donation + page `__ + that accepts donations for software projects and gives donation + receipts. + +- The + `survey `__ + that gives users who answer a question a small reward. + +Architecture overview +--------------------- + +The Taler software stack for a merchant consists of the following main +components: + +- frontend + A frontend which interacts with the customer’s browser. The frontend + enables the customer to build a shopping cart and place an order. + Upon payment, it triggers the respective business logic to satisfy + the order. This component is not included with Taler, but rather + assumed to exist at the merchant. This tutorial describes how to + develop a Taler frontend. + +- backend + A Taler-specific payment backend which makes it easy for the frontend + to process financial transactions with Taler. For this tutorial, you + will use a public sandbox backend. For production use, you must + either set up your own backend or ask another person to do so for + you. + +The following image illustrates the various interactions of these key +components: + +|image0| + +The backend provides the cryptographic protocol support, stores +Taler-specific financial information and communicates with the GNU Taler +exchange over the Internet. The frontend accesses the backend via a +RESTful API. As a result, the frontend never has to directly communicate +with the exchange, and also does not deal with sensitive data. In +particular, the merchant’s signing keys and bank account information are +encapsulated within the Taler backend. + +Some functionality of the backend (the “public interface“) is also +exposed to the customer’s browser directly. In the HTTP API, all public +endpoints are prefixed with ``/public/``. + +Public Sandbox Backend and Authentication +----------------------------------------- + +sandbox +authorization +How the frontend authenticates to the Taler backend depends on the +configuration. See Taler Merchant Operating Manual. + +The public sandbox backend https://backend.demo.taler.net/ uses an API +key in the ``Authorization`` header. The value of this header must be +``ApiKey sandbox`` for the public sandbox backend. + +:: + + >>> import requests + >>> requests.get("https://backend.demo.taler.net", + ... headers={"Authorization": "ApiKey sandbox"}) + + +If an HTTP status code other than 200 is returned, something went wrong. +You should figure out what the problem is before continuing with this +tutorial. + +The sandbox backend https://backend.demo.taler.net/ uses ``KUDOS`` as an +imaginary currency. Coins denominated in ``KUDOS`` can be withdrawn from +https://bank.demo.taler.net/. + +Merchant Instances +------------------ + +instance +The same Taler merchant backend server can be used by multiple separate +merchants that are separate business entities. Each of these separate +business entities is called a *merchant instance*, and is identified by +an alphanumeric *instance id*. If the instance is omitted, the instance +id ``default`` is assumed. + +The following merchant instances are configured on +https://backend.demo.taler.net/: + +- ``GNUnet`` (The GNUnet project) + +- ``FSF`` (The Free Software Foundation) + +- ``Tor`` (The Tor Project) + +- ``default`` (Kudos Inc.) + +Note that these are fictional merchants used for our demonstrators and +not affiliated with or officially approved by the respective projects. + +.. _Accepting-a-Simple-Payment: + +Accepting a Simple Payment +========================== + +Creating an Order for a Payment +------------------------------- + +order +Payments in Taler revolve around an *order*, which is a machine-readable +description of the business transaction for which the payment is to be +made. Before accepting a Taler payment as a merchant you must create +such an order. + +This is done by posting a JSON object to the backend’s ``/order`` API +endpoint. At least the following fields must be given: + +- amount: The amount to be paid, as a string in the format + ``CURRENCY:DECIMAL_VALUE``, for example ``EUR:10`` for 10 Euros or + ``KUDOS:1.5`` for 1.5 KUDOS. + +- summary: A human-readable summary for what the payment is about. The + summary should be short enough to fit into titles, though no hard + limit is enforced. + +- fulfillment_url: A URL that will be displayed once the payment is + completed. For digital goods, this should be a page that displays the + product that was purchased. On successful payment, the wallet + automatically appends the ``order_id`` as a query parameter, as well + as the ``session_sig`` for session-bound payments (discussed later). + +Orders can have many more fields, see `The Taler Order +Format <#The-Taler-Order-Format>`__. + +After successfully ``POST``\ ing to ``/order``, an ``order_id`` will be +returned. Together with the merchant ``instance``, the order id uniquely +identifies the order within a merchant backend. + +:: + + >>> import requests + >>> order = dict(order=dict(amount="KUDOS:10", + ... summary="Donation", + ... fulfillment_url="https://example.com/thanks.html")) + >>> order_resp = requests.post("https://backend.demo.taler.net/order", json=order, + ... headers={"Authorization": "ApiKey sandbox"}) + + +The backend will fill in some details missing in the order, such as the +address of the merchant instance. The full details are called the +*contract terms*. contract terms + +Checking Payment Status and Prompting for Payment +------------------------------------------------- + +The status of a payment can be checked with the ``/check-payment`` +endpoint. If the payment is yet to be completed by the customer, +``/check-payment`` will give the frontend a URL (the +payment_redirect_url) that will trigger the customer’s wallet to execute +the payment. + +Note that the only way to obtain the payment_redirect_url is to check +the status of the payment, even if you know that the user did not pay +yet. + +:: + + >>> import requests + >>> r = requests.get("https://backend.demo.taler.net/check-payment", + ... params=dict(order_id=order_resp.json()["order_id"]), + ... headers={"Authorization": "ApiKey sandbox"}) + >>> print(r.json()) + +If the paid field in the response is ``true``, the other fields in the +response will be different. Once the payment was completed by the user, +the response will contain the following fields: + +- paid: Set to true. + +- contract_terms: The full contract terms of the order. + +- refunded: ``true`` if a (possibly partial) refund was granted for + this purchase. + +- refunded_amount: Amount that was refunded + +- last_session_id: Last session ID used by the customer’s wallet. See + `Session-Bound Payments <#Session_002dBound-Payments>`__. + +Once the frontend has confirmed that the payment was successful, it +usually needs to trigger the business logic for the merchant to fulfill +the merchant’s obligations under the contract. + +.. _Giving-Refunds: + +Giving Refunds +============== + +refunds +A refund in GNU Taler is a way to “undo” a payment. It needs to be +authorized by the merchant. Refunds can be for any fraction of the +original amount paid, but they cannot exceed the original payment. +Refunds are time-limited and can only happen while the exchange holds +funds for a particular payment in escrow. The time during which a refund +is possible can be controlled by setting the ``refund_deadline`` in an +order. The default value for this refund deadline is specified in the +configuration of the merchant’s backend. + +The frontend can instruct the merchant backend to authorize a refund by +``POST``\ ing to the ``/refund`` endpoint. + +The refund request JSON object has the following fields: + +- order_id: Identifies for which order a customer should be refunded. + +- instance: Merchant instance to use. + +- refund: Amount to be refunded. If a previous refund was authorized + for the same order, the new amount must be higher, otherwise the + operation has no effect. The value indicates the total amount to be + refunded, *not* an increase in the refund. + +- reason: Human-readable justification for the refund. The reason is + only used by the Back Office and is not exposed to the customer. + +If the request is successful (indicated by HTTP status code 200), the +response includes a ``refund_redirect_url``. The frontend must redirect +the customer’s browser to that URL to allow the refund to be processed +by the wallet. + +This code snipped illustrates giving a refund: + +:: + + >>> import requests + >>> refund_req = dict(order_id="2018.058.21.46.06-024C85K189H8P", + ... refund="KUDOS:10", + ... instance="default", + ... reason="Customer did not like the product") + >>> requests.post("https://backend.demo.taler.net/refund", json=refund_req, + ... headers={"Authorization": "ApiKey sandbox"}) + + +.. _Giving-Customers-Tips: + +Giving Customers Tips +===================== + +tips +GNU Taler allows Web sites to grant small amounts directly to the +visitor. The idea is that some sites may want incentivize actions such +as filling out a survey or trying a new feature. It is important to note +that tips are not enforceable for the visitor, as there is no contract. +It is simply a voluntary gesture of appreciation of the site to its +visitor. However, once a tip has been granted, the visitor obtains full +control over the funds provided by the site. + +The “merchant” backend of the site must be properly configured for +tipping, and sufficient funds must be made available for tipping See +Taler Merchant Operating Manual. + +To check if tipping is configured properly and if there are sufficient +funds available for tipping, query the ``/tip-query`` endpoint: + +:: + + >>> import requests + >>> requests.get("https://backend.demo.taler.net/tip-query?instance=default", + ... headers={"Authorization": "ApiKey sandbox"}) + + +authorize tip +To authorize a tip, ``POST`` to ``/tip-authorize``. The following fields +are recognized in the JSON request object: + +- amount: Amount that should be given to the visitor as a tip. + +- instance: Merchant instance that grants the tip (each instance may + have its own independend tipping funds configured). + +- justification: Description of why the tip was granted. Human-readable + text not exposed to the customer, but used by the Back Office. + +- next_url: The URL that the user’s browser should be redirected to by + the wallet, once the tip has been processed. + +The response from the backend contains a ``tip_redirect_url``. The +customer’s browser must be redirected to this URL for the wallet to pick +up the tip. pick up tip + +This code snipped illustrates giving a tip: + +:: + + >>> import requests + >>> tip_req = dict(amount="KUDOS:0.5", + ... instance="default", + ... justification="User filled out survey", + ... next_url="https://merchant.com/thanks.html") + >>> requests.post("https://backend.demo.taler.net/tip-authorize", json=tip_req, + ... headers={"Authorization": "ApiKey sandbox"}) + + +.. _Advanced-topics: + +Advanced topics +=============== + +.. _Detecting-the-Presence-of-the-Taler-Wallet: + +Detecting the Presence of the Taler Wallet +------------------------------------------ + +wallet +Taler offers ways to detect whether a user has the wallet installed in +their browser. This allows Web sites to adapt accordingly. Note that not +all platforms can do presence detection reliably. Some platforms might +have a Taler wallet installed as a separate App instead of using a Web +extension. In these cases, presence detection will fail. Thus, sites may +want to allow users to request Taler payments even if a wallet could not +be detected, especially for visitors using mobiles. + +Presence detection without JavaScript +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Presence detection without JavaScript is based on CSS classes. You can +hide or show elements selectively depending on whether the wallet is +detected or not. + +In order to work correctly, a special fallback stylesheet must be +included that will be used when the wallet is not present. The +stylesheet can be put into any file, but must be included via a ``link`` +tag with the ``id`` attribute set to ``taler-presence-stylesheet``. If a +wallet is present, it will “hijack” this stylesheet to change how +elements with the following classes are rendered: + +The following CSS classes can be used: + +``taler-installed-hide`` + A CSS rule will set the ``display`` property for this class to + ``none`` once the Taler wallet is installed and enabled. If the + wallet is not installed, ``display`` will be ``inherit``. + +``taler-installed-show`` + A CSS rule will set the ``display`` property for this class to + ``inherit`` once the Taler wallet is installed and enabled. If the + wallet is not installed, ``display`` will be ``none``. + +The following is a complete example: + +:: + + + + + Tutorial + + + +

+ No wallet found. +

+

+ Wallet found! +

+ + + +The ``taler-fallback.css`` is part of the Taler’s *web-common* +repository, available at +https://git.taler.net/web-common.git/tree/taler-fallback.css. You may +have to adjust the ``href`` attribute in the HTML code above to point to +the correct location of the ``taler-fallback.css`` file on your Web +site. + +Detection with JavaScript +~~~~~~~~~~~~~~~~~~~~~~~~~ + +The following functions are defined in the ``taler`` namespace of the +``taler-wallet-lib`` helper library available at +https://git.taler.net/web-common.git/tree/taler-wallet-lib.js. + +``onPresent(callback: () => void)`` + Adds a callback to be called when support for Taler payments is + detected. + +``onAbsent(callback: () => void)`` + Adds a callback to be called when support for Taler payments is + disabled. + +Note that the registered callbacks may be called more than once. This +may happen if a user disables or enables the wallet in the browser’s +extension settings while a shop’s frontend page is open. + +.. _Integration-with-the-Back-Office: + +Integration with the Back Office +-------------------------------- + +Taler ships a Back Office application as a stand-alone Web application. +The Back Office has its own documentation at +https://docs.taler.net/backoffice/html/manual.html. + +Developers wishing to tightly integrate back office support for +Taler-based payments into an existing back office application should +focus on the wire transfer tracking and transaction history sections of +the Taler Backend API specification at +https://docs.taler.net/api/api-merchant.html + +.. _Session_002dBound-Payments: + +Session-Bound Payments +---------------------- + +session +Sometimes checking if an order has been paid for is not enough. For +example, when selling access to online media, the publisher may want to +be paid for exactly the same product by each customer. Taler supports +this model by allowing the mechant to check whether the “payment +receipt” is available on the user’s current device. This prevents users +from easily sharing media access by transmitting a link to the +fulfillment page. Of course sophisticated users could share payment +receipts as well, but this is not as easy as sharing a link, and in this +case they are more likely to just share the media directly. + +To use this feature, the merchant must first assign the user’s current +browser an ephemeral ``session_id``, usually via a session cookie. When +executing or re-playing a payment, the wallet will receive an additional +signature (``session_sig``). This signature certifies that the wallet +showed a payment receipt for the respective order in the current +session. cookie + +Session-bound payments are triggerd by passing the ``session_id`` +parameter to the ``/check-payment`` endpoint. The wallet will then +redirect to the fulfillment page, but include an additional +``session_sig`` parameter. The frontend can query ``/check-payment`` +with both the ``session_id`` and the ``session_sig`` to verify that the +signature is correct. + +The last session ID that was successfuly used to prove that the payment +receipt is in the user’s wallet is also available as ``last_session_id`` +in the response to ``/check-payment``. + +.. _Product-Identification: + +Product Identification +---------------------- + +resource url +In some situations the user may have paid for some digital good, but the +frontend does not know the exact order ID, and thus cannot instruct the +wallet to reveil the existing payment receipt. This is common for simple +shops without a login system. In this case, the user would be prompted +for payment again, even though they already purchased the product. + +To allow the wallet to instead find the existing payment receipt, the +shop must use a unique fulfillment URL for each product. Then, the +frontend must provide an additional ``resource_url`` parameter to to +``/check-payment``. It should identify this unique fulfillment URL for +the product. The wallet will then check whether it has paid for a +contract with the same ``resource_url`` before, and if so replay the +previous payment. + +.. _The-Taler-Order-Format: + +The Taler Order Format +---------------------- + +contract +terms +order +A Taler order can specify many details about the payment. This section +describes each of the fields in depth. + +Financial amounts are always specified as a string in the format +``"CURRENCY:DECIMAL_VALUE"``. + +amount + amount + Specifies the total amount to be paid to the merchant by the + customer. + +max_fee + fees + maximum deposit fee + This is the maximum total amount of deposit fees that the merchant is + willing to pay. If the deposit fees for the coins exceed this amount, + the customer has to include it in the payment total. The fee is + specified using the same triplet used for amount. + +max_wire_fee + fees + maximum wire fee + Maximum wire fee accepted by the merchant (customer share to be + divided by the ’wire_fee_amortization’ factor, and further reduced if + deposit fees are below ’max_fee’). Default if missing is zero. + +wire_fee_amortization + fees + maximum fee amortization + Over how many customer transactions does the merchant expect to + amortize wire fees on average? If the exchange’s wire fee is above + ’max_wire_fee’, the difference is divided by this number to compute + the expected customer’s contribution to the wire fee. The customer’s + contribution may further be reduced by the difference between the + ’max_fee’ and the sum of the actual deposit fees. Optional, default + value if missing is 1. 0 and negative values are invalid and also + interpreted as 1. + +pay_url + pay_url + Which URL accepts payments. This is the URL where the wallet will + POST coins. + +fulfillment_url + fulfillment URL + Which URL should the wallet go to for obtaining the fulfillment, for + example the HTML or PDF of an article that was bought, or an order + tracking system for shipments, or a simple human-readable Web page + indicating the status of the contract. + +order_id + order ID + Alphanumeric identifier, freely definable by the merchant. Used by + the merchant to uniquely identify the transaction. + +summary + summary + Short, human-readable summary of the contract. To be used when + displaying the contract in just one line, for example in the + transaction history of the customer. + +timestamp + Time at which the offer was generated. + +pay_deadline + payment deadline + Timestamp of the time by which the merchant wants the exchange to + definitively wire the money due from this contract. Once this + deadline expires, the exchange will aggregate all deposits where the + contracts are past the refund_deadline and execute one large wire + payment for them. Amounts will be rounded down to the wire transfer + unit; if the total amount is still below the wire transfer unit, it + will not be disbursed. + +refund_deadline + refund deadline + Timestamp until which the merchant willing (and able) to give refunds + for the contract using Taler. Note that the Taler exchange will hold + the payment in escrow at least until this deadline. Until this time, + the merchant will be able to sign a message to trigger a refund to + the customer. After this time, it will no longer be possible to + refund the customer. Must be smaller than the pay_deadline. + +products + product description + Array of products that are being sold to the customer. Each entry + contains a tuple with the following values: + + description + Description of the product. + + quantity + Quantity of the items to be shipped. May specify a unit (``1 kg``) + or just the count. + + price + Price for quantity units of this product shipped to the given + delivery_location. Note that usually the sum of all of the prices + should add up to the total amount of the contract, but it may be + different due to discounts or because individual prices are + unavailable. + + product_id + Unique ID of the product in the merchant’s catalog. Can generally + be chosen freely as it only has meaning for the merchant, but + should be a number in the range :math:`[0,2^{51})`. + + taxes + Map of applicable taxes to be paid by the merchant. The label is + the name of the tax, i.e. VAT, sales tax or income tax, and the + value is the applicable tax amount. Note that arbitrary labels are + permitted, as long as they are used to identify the applicable tax + regime. Details may be specified by the regulator. This is used to + declare to the customer which taxes the merchant intends to pay, + and can be used by the customer as a receipt. The information is + also likely to be used by tax audits of the merchant. + + delivery_date + Time by which the product is to be delivered to the + delivery_location. + + delivery_location + This should give a label in the locations map, specifying where + the item is to be delivered. + + Values can be omitted if they are not applicable. For example, if a + purchase is about a bundle of products that have no individual prices + or product IDs, the product_id or price may not be specified in the + contract. Similarly, for virtual products delivered directly via the + fulfillment URI, there is no delivery location. + +merchant + address + This should give a label in the locations map, specifying where + the merchant is located. + + name + This should give a human-readable name for the merchant’s + business. + + jurisdiction + This should give a label in the locations map, specifying the + jurisdiction under which this contract is to be arbitrated. + +locations + location + Associative map of locations used in the contract. Labels for + locations in this map can be freely chosen and used whenever a + location is required in other parts of the contract. This way, if the + same location is required many times (such as the business address of + the customer or the merchant), it only needs to be listed (and + transmitted) once, and can otherwise be referred to via the label. A + non-exhaustive list of location attributes is the following: + + country + Name of the country for delivery, as found on a postal package, + i.e. “France”. + + state + Name of the state for delivery, as found on a postal package, i.e. + “NY”. + + region + Name of the region for delivery, as found on a postal package. + + province + Name of the province for delivery, as found on a postal package. + + city + Name of the city for delivery, as found on a postal package. + + ZIP code + ZIP code for delivery, as found on a postal package. + + street + Street name for delivery, as found on a postal package. + + street number + Street number (number of the house) for delivery, as found on a + postal package. + + name receiver name for delivery, either business or person name. + + Note that locations are not required to specify all of these fields, + and they is also allowed to have additional fields. Contract + renderers must render at least the fields listed above, and should + render fields that they do not understand as a key-value list. + +.. _GNU_002dLGPL: + +GNU-LGPL +======== + +license +LGPL +Version 2.1, February 1999 +:: + + Copyright © 1991, 1999 Free Software Foundation, Inc. + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + [This is the first released version of the Lesser GPL. It also counts + as the successor of the GNU Library Public License, version 2, hence the + version number 2.1.] + +**Preamble** + +The licenses for most software are designed to take away your freedom to +share and change it. 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