..
  This file is part of GNU Taler.

  Copyright (C) 2021 Taler Systems SA

  GNU 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.

  GNU 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
  GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>

  @author Florian Dold

GNU Taler Exchange Setup Guide
##############################

This setup guide walks a system administrator through all steps required to
install an exchange and check that it is functional.  For more background,
please read the Operator Manual.


System Requirements
===================

This guide assumes that you are running Ubuntu 20.04 (Focal Fossa).

We recommend the setup of offline signing keys to be done on a second machine that
does not have internet access.

In the guide, we mark commands that are supposed to be executed on the online
exchange machine as ``[root@exchange-online]#`` / ``[$user@exchange-online]$`` and commands for the offline
machine as ``[root@exchange-offline]#`` / ``[$user@exchange-offline]$``.  It is possible to do the entire setup
on one machine, but we do not recommend this for security reasons.


Before you start
================

To deploy this with a real bank, you need:

* IBAN of the bank account to use
* BIC of the bank
* EBICS host, user and partner IDs

Information to write down during the installation:

* libeufin nexus superuser password
* Taler facade base URL
* exchange nexus username and password



Installation
============

We assume that the system is a minimal installation of Ubuntu 20.04 LTS.
Ideally, you should have two hosts, ``exchange-online`` and
``exchange-offline``.  It is also possible to run the HTTPS nginx server or
the Postgres database on yet another host, but in these instructions we will
assume that only two hosts are used. Alas, the instructions will also work if
you run everything on one system, but then you have the security drawback of
not keeping the high-security private keys disconnected from the Internet.

To install the exchange, first make sure that your system is up-to-date
and that the ``gnupg`` package has been installed.

.. code-block:: shell-session

  [root@exchange-online]# apt-get update
  [root@exchange-online]# apt-get upgrade

Next, add the ``focal-fossa`` apt repository provided by Taler Systems S.A. to
your package sources:

.. code-block:: shell-session

  [root@exchange-online]# cat > /etc/apt/sources.list.d/taler.list <<EOF
  deb https://deb.taler.net/apt/ubuntu focal-fossa main
  EOF

Before installing Taler packages, you need to add the Taler Systems S.A. package
signing key to your list of trusted keys and update the package index:

.. code-block:: shell-session

  [root@exchange-online]# wget -O - https://taler.net/taler-systems.gpg.key | apt-key add -
  [root@exchange-online]# apt-get update

..
  FIXME: this happens after the update.
  N: Skipping acquire of configured file 'main/binary-i386/Packages' as repository 'https://deb.taler.net/apt/ubuntu focal-fossa InRelease' doesn't support architecture 'i386'

Finally, the required packages can be installed:


.. code-block:: shell-session

  [root@exchange-online]# apt-get install -y nginx postgresql
  [root@exchange-online]# apt-get install -y taler-exchange taler-exchange-offline
  [root@exchange-online]# apt-get install -y taler-merchant taler-wallet-cli

When asked about using dbconfig to configure the merchant's database,
select ``yes``.

By default, all installed services will be disabled.  You need to enable
and start them later.

While ``taler-merchant`` and ``taler-wallet`` are not required to operate an
exchange, they are useful for testing.


Configuration Basics
====================

The configuration for all Taler components uses a single configuration file
as entry point: ``/etc/taler/taler.conf``.

System defaults are automatically loaded from files in
``/usr/share/taler/config.d``.  These default files should never be modified.

The default configuration ``taler.conf`` configuration file also includes all
configuration files in ``/etc/taler/conf.d``.  The settings from files in
``conf.d`` are only relevant to particular components of Taler, while
``taler.conf`` contains settings that affect all components.


The directory ``/etc/taler/secrets`` contains configuration file snippets with
values that should only be readable to certain users.  They are included with the ``@inline-secret@``
directive and should end with ``.secret.conf``.

To view the entire configuration annotated with the source of each configuration option, you
can use the ``taler-config`` helper:

..
  FIXME: mostly all the configuration files are owned root:root.  Is that wanted?
  Wasn't taler-exchange-httpd supposed to own those? CG: Well, for MOST of the configuration files, root-ownage is OK, but I agree that merchant-db.secret.conf and exchange-accountcredentials.secret.conf have the wrong roup owner and permissions, and exchange-db.secret.conf should probably be 640 instead of 660.

.. code-block:: shell-session

  [root@exchange-online]# taler-config --diagnostics
  < ... annotated, full configuration ... >

.. warning::

  While ``taler-config`` also supports rewriting configuration files, we strongly
  recommend to edit configuration files manually, as ``taler-config`` does not
  preserve comments and, by default, rewrites ``/etc/taler/taler.conf``.


Services, users, groups and file system hierarchy
=================================================

The *taler-exchange-httpd* package will create several system users
to compartmentalize different parts of the system:

* taler-exchange-httpd: runs the HTTP daemon with the core business logic
* taler-exchange-secmod-rsa: manages the RSA private online signing keys
* taler-exchange-secmod-eddsa: manages the EdDSA private online signing keys
* taler-exchange-closer: closes idle reserves by triggering wire transfers that refund the originator
* taler-exchange-aggregator: aggregates deposits into larger wire transfer requests
* taler-exchange-wire: performs wire transfers with the bank (via libeufin/nexus)
* postgres: runs the Postgres database (from *postgres* package)
* www-data: runs the frontend HTTPS service with the TLS keys (from *nginx* package)

.. note::

   The *taler-merchant-httpd* package additionally creates a taler-merchant-httpd user
   to runs the HTTP daemon with the merchant business logic.


The exchange setup uses the following system groups:

* taler-exchange-db: group for all Taler users with direct database access, specifically taler-exchange-httpd, taler-exchange-wire, taler-exchange-closer and taler-exchange-aggregator
* taler-exchange-secmod: group for processes with access to online signing keys, so taler-exchange-secmod-rsa, taler-exchange-secmod-eddsa and taler-exchange-httpd
* taler-exchange-offline: group for the access to the offline private key (only used on the offline host and not used on the online system)

..
  FIXME: "taler-exchange-secmod: group for processes with access to online signing keys, so taler-exchange-secmod-rsa, taler-exchange-secmod-eddsa and taler-exchange-httpd .... what?"  Seems that this sentence lacks conclusion.



The package will deploy systemd service files in
``/usr/lib/systemd/system/`` for the various components:

* taler-exchange-aggregator.service: service that schedules wire transfers which combine multiple deposits to the same merchant
* taler-exchange-closer.service: service that watches for reserves that have been abandoned and schedules wire transfers to send the money back to the originator
* taler-exchange-httpd.service: main Taler exchange logic with the public REST API
* taler-exchange-httpd.socket: systemd socket activation for the Taler exchange HTTP daemon
* taler-exchange-secmod-eddsa.service: software security module for making EdDSA signatures
* taler-exchange-secmod-rsa.service: software security module for making RSA signatures
* taler-exchange-transfer.service: service that triggers outgoing wire transfers (pays merchants)
* taler-exchange-wirewatch.service: service that watches for incoming wire transfers (first step of withdraw)
* taler-exchange.target: Main target for the Taler exchange to be operational


The deployment creates the following key locations in the system:

* /etc/taler/: configuration files
* /var/run/taler/: contains the UNIX domain sockets for inter-process communication (IPC)
* /var/lib/taler/: serves as the $HOME for all Taler users and contains sub-directories
  with the private keys; which keys are stored here depends on the host:

  * online system: exchange-secmod-eddsa and exchange-secmod-rsa keys
  * offline system: exchange-offline keys


Setup Linting
=============

The ``taler-wallet-cli`` package comes with a experimental tool that runs various
checks on the current GNU Taler exchange deployment:

.. code-block:: shell-session

  [root@exchange-online]# taler-wallet-cli deployment lint-exchange

You can optionally pass the ``--debug`` option to get more verbose output, and
``--continue`` to continue with further checks even though a previous one has
failed.

Basic Setup: Currency and Denominations
=======================================

A Taler exchange only supports a single currency.  The currency
and the smallest currency unit supported by the bank system
must be specified in ``/etc/taler/taler.conf``.

.. code-block:: ini
  :caption: /etc/taler/taler.conf

   [taler]
   CURRENCY = EUR
   CURRENCY_ROUND_UNIT = EUR:0.01

   # ... rest of file ...

.. warning::

   When editing ``/etc/taler/taler.conf``, take care to not accidentally remove
   the @inline-matching@ directive to include the configuration files in ``conf.d``.

Next, the electronic cash denominations that the exchange offers must be
specified.  The ``taler-wallet-cli`` has a helper command that generates a
reasonable denomination structure.

.. code-block:: shell-session

  taler-wallet-cli deployment gen-coin-config --min-amount EUR:0.01 --max-amount EUR:100 > /etc/taler/conf.d/exchange-coins.conf

.. note::

   FIXME: change tool to not take currency from configuration, but instead
   to accept unit currency as the argument; (i.e. EUR:0.0025). Also take
   another argument for how many denominations to generate (2^XX). Finally,
   do use the unit currency as the default deposit fee.

You can manually review and edit the generated configuration file. The main
change that is possibly required is updating the various fees.


Wire Gateway Setup
==================

The Taler Wire Gateway is an API that connects the Taler exchange to
the underlying core banking system.

LibEuFin is an implementation of the Wire Gateway API for the EBICS protocol.
This section will walk through (1) installing and configuring LibEuFin and
(2) connecting the Taler Exchange to LibEuFin.

.. note::

   If you do not have a bank account with EBICS but want to test these instructions,
   you can use the EBICS sandbox as described in the
   :doc:`LibEuFin Tutorial <libeufin/nexus-tutorial>`


Installation and Basic Configuration
------------------------------------

First, install the ``libeufin`` package.  This can be done on the ``exchange-online``
machine or a different one.

.. code-block:: shell-session

  [root@exchange-online]# apt-get install -y libeufin

The main component of LibEuFin is called the Nexus.  It implements a Web
service that provides a JSON abstraction layer to access bank accounts.

The Nexus currently uses an sqlite3 database as storage by default.
We currently recommend to stick with this default.  In future
versions, there will be a migration path to a postgresql database.

The HTTP port and database connection string can be edited in the configuration:

.. code-block:: ini
  :caption: /etc/libeufin/nexus.env

  LIBEUFIN_NEXUS_PORT=5017
  LIBEUFIN_NEXUS_DB_CONNECTION=jdbc:sqlite:/var/lib/libeufin/nexus/nexus-db.sqlite3

After configuring the database, you can start the service.
The database is initialized automatically, there is no ``dbinit`` command
for the LibEuFin nexus.

..
  FIXME: 'dbinit' isn't a (exact) name for exchane and merchant, but this way
  the reader might wrongly think it is.  Also, steps that should NOT be taken
  could - by not being mentioned - spare time (to the reader) and space to the
  document.  So the part after comma for me can be removed.

.. code-block:: shell-session

   [root@exchange-online]# systemctl enable libeufin-nexus
   [root@exchange-online]# systemctl start libeufin-nexus

You can now create a superuser account.  The command to
create the superuser needs direct database access, thus
the configuration file is sourced first, and the relevant
environment variable is exported.

.. code-block:: console

  [root@exchange-online]# source /etc/libeufin/nexus.env
  [root@exchange-online]# export LIBEUFIN_NEXUS_DB_CONNECTION
  [root@exchange-online]# NEXUS_ADMIN_PW=$(tr -dc A-Za-z0-9 </dev/urandom | head -c 13)
  [root@exchange-online]# libeufin-nexus superuser admin --password $NEXUS_ADMIN_PW

If you omit ``--password $NEXUS_ADMIN_PW``, you will interactively be asked for a password.
For simplicity, a superuser can as well act as a normal user, but an API
to create less privileged users is offered.

.. note::

  User and permissions management in LibEuFin is still under development.
  In particular, permissions for non-superusers are very limited at the moment.


Connecting Nexus with an EBICS account
--------------------------------------

The command line interface of the LibEuFin nexus needs the following three
values to be defined in the environment: ``LIBEUFIN_NEXUS_URL``,
``LIBEUFIN_NEXUS_USERNAME``, and ``LIBEUFIN_NEXUS_PASSWORD``.  In this example,
``LIBEUFIN_NEXUS_USERNAME`` should be set to ``admin``, and
``LIBEUFIN_NEXUS_PASSWORD`` to the value hold in ``NEXUS_ADMIN_PW`` from the
previous step (the ``libeufin-nexus superuser`` command).  The
``LIBEUFIN_NEXUS_URL`` could be given as ``http://localhost:5017/``.

Next, we create a EBICS *bank connection* that nexus can use to communicate with the bank.

.. code-block:: console

  [root@exchange-online]# libeufin-cli \
      connections \
        new-ebics-connection \
          --ebics-url $EBICS_BASE_URL \
          --host-id $EBICS_HOST_ID \
          --partner-id $EBICS_PARTNER_ID \
          --ebics-user-id $EBICS_USER_ID \
          $CONNECTION_NAME

If this step executes correctly, Nexus will have created all the cryptographic
material that is needed on the client side; in this EBICS example, it created
the signature and identification keys.  It is therefore advisable to *make
a backup copy* of such keys.

.. code-block:: console

  [root@exchange-online]# libeufin-cli \
      connections \
        export-backup \
          --passphrase $SECRET \
          --output-file $BACKUP_FILE \
          $CONNECTION_NAME

At this point, Nexus needs to both communicate its keys to the bank, and
download the bank's keys.  This syncronization happens through the INI, HIA, and
finally, HPB message types.

After the electronic synchronization, the subscriber must confirm their keys
by sending a physical mail to the bank.  The following command helps generating
such letter:

.. code-block:: console

  [root@exchange-online]# libeufin-cli connections get-key-letter $CONNECTION_NAME out.pdf

.. code-block:: console

  [root@exchange-online]# libeufin-cli \
      connections \
        connect \
          $CONNECTION_NAME

..
  FIXME: maybe is not 100% clear that 'connecting' means exchanging keys
  wiht the bank?

Once the connection is synchronized, Nexus needs to import locally the data
corresponding to the bank accounts offered by the bank connection just made.
The command below downloads the list of the bank accounts offered by ``$CONNECTION_NAME``.

.. code-block:: console

  [root@exchange-online]# libeufin-cli \
      connections \
        download-bank-accounts \
          $CONNECTION_NAME

It is now possible to list the accounts offered by the connection.

.. code-block:: console

  [root@exchange-online]# libeufin-cli \
      connections \
        list-offered-bank-accounts \
          $CONNECTION_NAME

.. note::

   The ``nexusBankAccountId`` field should at this step be ``null``,
   as we have not yet imported the bank account and thus the account
   does not yet have a local name.

Nexus now needs an explicit import of the accounts it should manage.  This
step is needed to let the user pick a custom name for such accounts.

.. code-block:: console

  [root@exchange-online]# libeufin-cli \
      connections \
        import-bank-account \
          --offered-account-id testacct01 \
          --nexus-bank-account-id $LOCAL_ACCOUNT_NAME \
          $CONNECTION_NAME

Once a Nexus user imported a bank account (``$LOCAL_ACCOUNT_NAME``)
under a certain connection (``$CONNECTION_NAME``), it is possible
to accomplish the usual operations for any bank account: asking for the
list of transactions, and making a payment.

Testing: Requesting the transaction history
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The LibEuFin nexus keeps a local copy of the bank account's transaction
history.  Before querying transactions locally, it is necessary
to request transactions for the bank account via the bank connection.

This command asks Nexus to download the latest transaction reports/statements
through the bank connection:

.. code-block:: console

  [root@exchange-online]# libeufin-cli accounts fetch-transactions $LOCAL_ACCOUNT_NAME

.. note::

   By default, the latest available transactions are fetched.  It is also
   possible to specify a custom date range (or even all available transactions)
   and the type of transactions to fetch (inter-day statements or intra-day
   reports).

..
  FIXME: possibly the date range filter is still missing, see #6243.

Once Nexus has stored all the information in the database, the
client can ask to actually see the transactions:

.. code-block:: console

  [root@exchange-online]# libeufin-cli accounts transactions $LOCAL_ACCOUNT_NAME

Testing: Making payments
~~~~~~~~~~~~~~~~~~~~~~~~

Payments pass through two phases: preparation and submission.  The preparation
phase assigns the payment initiation a unique ID, which prevents accidental
double submissions of payments in case of network failures or other
disruptions.


The following command prepares a payment:

.. code-block:: console

  [root@exchange-online]# libeufin-cli accounts prepare-payment \
          --creditor-iban=$IBAN_TO_SEND_MONEY_TO \
          --creditor-bic=$BIC_TO_SEND_MONEY_TO \
          --creditor-name=$CREDITOR_NAME \
          --payment-amount=$AMOUNT \
          --payment-subject=$SUBJECT \
          $LOCAL_ACCOUNT_NAME

Note: the ``$AMOUNT`` value needs the format ``X.Y:CURRENCY``; for example
``EUR:10``, or ``EUR:1.01``.

The previous command should return a value (``$UUID``) that uniquely
identifies the prepared payment in the Nexus system.  That is needed
in the next step, to **send the payment instructions to the bank**:

.. code-block:: console

  [root@exchange-online]# libeufin-cli accounts submit-payment \
        --payment-uuid $UUID \
        $LOCAL_ACCOUNT_NAME

Automatic scheduling
~~~~~~~~~~~~~~~~~~~~

With an EBICS bank connection, the LibEuFin nexus needs to regularly query for
new transactions and (re-)submit prepared payments.

It is possible to schedule these tasks via an external task scheduler such as
cron(8).  However, the nexus also has an internal task scheduling mechanism for
accounts.


The following three commands create a schedule for submitting payments hourly,
fetching transactions (intra-day reports) every 5 minutes, and (inter-day statements)
once at 11pm every day :

.. code-block:: console

   [root@exchange-online]# libeufin-cli accounts task-schedule $LOCAL_ACCOUNT_NAME \
       --task-type="submit" \
       --task-name='submit-payments-hourly' \
       --task-cronspec='0 0 *'

   [root@exchange-online]# libeufin-cli accounts task-schedule $LOCAL_ACCOUNT_NAME \
       --task-type="fetch" \
       --task-name='fetch-5min' \
       --task-cronspec='0 */5 *' \
       --task-param-level=report \
       --task-param-range-type=latest

   [root@exchange-online]# libeufin-cli accounts task-schedule $LOCAL_ACCOUNT_NAME \
       --task-type="fetch" \
       --task-name='fetch-daily' \
       --task-cronspec='0 0 23' \
       --task-param-level=statement \
       --task-param-range-type=latest

The cronspec has the following format, which is slightly non-standard due to
the ``SECONDS`` field

.. code-block:: none

  SECONDS MINUTES HOURS DAY-OF-MONTH[optional] MONTH[optional] DAY-OF-WEEK[optional]


Restoring a Backup
~~~~~~~~~~~~~~~~~~

The following command restores all the details associated with
one bank connection subscription.  For EBICS, this means that the
INI and HIA secret keys will be restored for the requesting user.

.. code-block:: console

  [root@exchange-online]# libeufin-cli connections \
      restore-backup \
      --passphrase=$SECRET \
      --backup-file=$BACKUP_FILE \
      $CONNECTION_NAME

..
  FIXME: this section, although useful, doesn't really belong
  to the flow here.  It is very unlikely that the reader needs
  to restore the backup just here.  Maybe move next to the create-backup
  command as a note, or simply remove it entirely from this guide.

  Also worth noting: on a bad password given, Nexus responds
  "bad backup given" instead of "authentication failed".

Creating a Taler facade
~~~~~~~~~~~~~~~~~~~~~~~

Facades are additional abstraction layers that can serve
specific purposes.  For example, one application might need
a filtered version of the transaction history, or it might
want to refuse payments that do not conform to certain rules.

At this moment, only the *Taler facade type* is implemented
in the Nexus, and the command below instantiates one under a
existing bank account / connection pair.  You can freely
assign an identifier for the ``$FACADE_NAME`` below:

.. code-block:: console

  [root@exchange-online]# libeufin-cli facades new-taler-wire-gateway-facade \
      --currency EUR \
      --facade-name $FACADE_NAME \
      $CONNECTION_NAME \
      $LOCAL_ACCOUNT_NAME

At this point, the additional *taler-wire-gateway* (FIXME: link
here to API here) API becomes offered by the Nexus.  The purpose
is to let a Taler exchange rely on Nexus to manage its bank account.

The base URL of the facade that can be used by the Taler exchange
as the Taler Wire Gateway base URL can be seen by listing the facades:

.. code-block:: console

  [root@exchange-online]# libeufin-cli facades list

Managing Permissions and Users
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This guide has so far assumed that a superuser is accessing the LibEuFin Nexus.
However, it is advisable that the Nexus is accessed with users that only have a
minimal set of permissions.

The Nexus currently only has support for giving non-superusers access to Taler
wire gateway facades.

To create a new user, use the ``users`` subcommand of the CLI:

.. code-block:: console

  [root@exchange-online]# libeufin-cli users list
  # [ ... shows available users ... ]

  [root@exchange-online]# libeufin-cli users create $USERNAME
  # [ ... will prompt for password ... ]

Permissions are managed with the ``permissions`` subcommand.
The following commands grant permissions to view the transaction history
and create payment initiations with a Taler wire gateway facade:


.. code-block:: console

  [root@exchange-online]# libeufin-cli permissions grant \
     user $USERNAME \
     facade $FACADENAME \
     facade.talerWireGateway.history

  [root@exchange-online]# libeufin-cli permissions grant \
     user $USERNAME \
     facade $FACADENAME \
     facade.talerWireGateway.transfer

..
  FIXME: the two commands above output a empty JSON object
  when successful.  Possibly, we should suppress that (just like
  the other commands do)

The list of all granted permissions can be reviewed:

.. code-block:: console

  [root@exchange-online]# libeufin-cli permissions list


Exchange Wire Configuration
---------------------------

The exchange must be configured with the right settings to
access the Taler Wire Gateway.  An exchange can be configured
to use multiple bank accounts by using multiple Wire Gateways.
Typically only one Wire Gateway is used.

A Taler Wire Gateway is configured in a configuration section that follows the
pattern ``exchange-account-$id``, where ``$id`` is an internal identifier for
the bank account accessed by the exchange.  The basic information for an account should
be put in ``/etc/taler/conf.d/exchange-business.conf``.
The secret credentials to access the Taler Wire Gateway API should
be put into a corresponding ``exchange-accountcredentials-$id`` section
in ``/etc/taler/secrets/exchange-accountcredentials.conf``.
The latter file
should already be only readable for the ``taler-exchange-wire`` user.  Other
exchange processes should not have access to this information.

.. code-block:: ini
  :caption: /etc/taler/conf.d/exchange-business.conf

  [exchange-account-1]
  enable_credit = yes
  enable_debit = yes

  # Account identifier in the form of an RFC-8905 payto:// URI
  # For SEPA, looks like payto://sepa/$IBAN
  payto_uri =

  @inline-secret@ exchange-accountcredentials-1 ../secrets/exchange-accountcredentials.secret.conf


.. code-block:: ini
  :caption: /etc/taler/secrets/exchange-accountcredentials.secret.conf

  [exchange-accountcredentials-1]

  # LibEuFin expects basic auth
  wire_gateway_auth_method = basic

  # username and password set in LibEuFin
  username = ...
  password = ...

  # base URL of the wire gateway set up with LibEuFin
  wire_gateway_url = ...


The Wire Gateway configuration can be tested with the following command:

.. code-block:: shell-session

   [root@exchange-online]# taler-exchange-wire-gateway-client \
     --section exchange-accountcredentials-1 --debit-history
   [root@exchange-online]# taler-exchange-wire-gateway-client \
     --section exchange-accountcredentials-1 --credit-history



Exchange Database Setup
=======================

The access credentials for the exchange's database are configured in
``/etc/taler/secrets/exchange-db.secret.conf``.  Currently, only postgres is
supported as a database backend.

The following users must have access to the exchange database:

* taler-exchange-httpd
* taler-exchange-wire
* taler-exchange-aggregator
* taler-exchange-closer

These users are all in the taler-exchange-db group, and the
``exchange-db.secret.conf`` should already be only readable by users in
this group.

To create a database for the Taler exchange on the local system, run:

.. code-block:: shell-session

  [root@exchange-online]# su - postgres
  [postgres@exchange-online]# createuser taler-exchange-httpd
  [postgres@exchange-online]# createuser taler-exchange-wire
  [postgres@exchange-online]# createuser taler-exchange-aggregator
  [postgres@exchange-online]# createuser taler-exchange-closer
  [postgres@exchange-online]# createdb -O taler-exchange-httpd taler-exchange
  [postgres@exchange-online]# exit

This will create a ``taler-exchange`` database owned by the
``taler-exchange-httpd`` user.  We will use that user later to perform
database maintenance operations.


Assuming the above database setup, the database credentials to configure
in the configuration file would simply be:

.. code-block:: ini
  :caption: /etc/taler/secrets/exchange-db.secret.conf

  [exchangedb-postgres]
  CONFIG=postgres:///taler-exchange


If the database is run on a different host, please follow the instructions
from the Postgres manual for configuring remote access.

After configuring the database credentials, the exchange database needs
to be initialized with the following command:

.. code-block:: shell-session

  [root@exchange-online]# sudo -u taler-exchange-httpd taler-exchange-dbinit

Finally we need to grant the other accounts limited access:

.. code-block:: shell-session

  [root@exchange-online]# echo 'GRANT SELECT,INSERT,UPDATE ON ALL TABLES IN SCHEMA public TO "taler-exchange-aggregator";' \
    | sudo -u taler-exchange-httpd psql taler-exchange
  [root@exchange-online]# echo 'GRANT SELECT,INSERT,UPDATE ON ALL TABLES IN SCHEMA public TO "taler-exchange-closer";' \
    | sudo -u taler-exchange-httpd psql taler-exchange
  [root@exchange-online]# echo 'GRANT SELECT,INSERT,UPDATE ON ALL TABLES IN SCHEMA public TO "taler-exchange-wire";' \
    | sudo -u taler-exchange-httpd psql taler-exchange
  [root@exchange-online]# echo 'GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO "taler-exchange-aggregator";' \
    | sudo -u taler-exchange-httpd psql taler-exchange
  [root@exchange-online]# echo 'GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO "taler-exchange-closer";' \
    | sudo -u taler-exchange-httpd psql taler-exchange
  [root@exchange-online]# echo 'GRANT USAGE ON ALL SEQUENCES IN SCHEMA public TO "taler-exchange-wire";' \
    | sudo -u taler-exchange-httpd psql taler-exchange

..
  FIXME: the above commands do work, except that they produce a eye-unfriendly "cannot change to /root directory"
  message after the execution.  This might be avoided by first getting a shell as the taler-exchange-httpd user
  and then run the SQL statements.

.. note::

   The above instructions for changing database permissions only work *after*
   having initialized the database with ``taler-exchange-dbinit``, as
   the tables to exist before permissions can be granted on them.

..

  FIXME: Why don't we grant the permissions to the schema / database then?



Offline Signing Setup
=====================

The offline signing keys of the exchange should be stored on a different machine.
The responsibilities of this offline signing machine are:

* generation of the exchange's offline master signing key
* secure storage of the exchange's offline master signing key
* generation of certificates (signed with the offline master signing key) that will be imported by the exchange


.. code-block:: shell-session

  [root@exchange-offline]# sudo -u taler-exchange-offline taler-exchange-offline setup
  < ... prints the exchange master public key >

The public key printed as the output of this command must be put into the configuration
of the online machine:

.. code-block:: ini
  :caption: /etc/taler/conf.d/exchange-business.conf

   [exchange]
   MASTER_PUBLIC_KEY = YE6Q6TR1ED...

   # ... rest of file ...


Exchange Web service / API Setup
================================

By default, the ``taler-exchange-httpd`` service listens for HTTP connections
on a UNIX domain socket.  To make the service publicly available, a reverse
proxy such as nginx should be used.  We strongly recommend to configure nginx
to use TLS.

The public URL that the exchange will be served under should
be put in ``/etc/taler/conf.d/exchange-business.conf`` configuration file.

.. code-block:: ini
  :caption: /etc/taler/conf.d/exchange-business.conf

   [exchange]
   BASE_URL = https://example.com/

   # ... rest of file ...

The ``taler-exchange`` package ships with a sample configuration that can be
enabled in nginx:

.. code-block:: shell-session

  [root@exchange-online]# vim /etc/nginx/sites-available/taler-exchange
  < ... customize configuration ... >
  [root@exchange-online]# ln -s /etc/nginx/sites-available/taler-exchange \
                                /etc/nginx/sites-enabled/taler-exchange
  [root@exchange-online]# systemctl reload nginx


The exchange HTTP service can now be started:

.. code-block:: shell-session

  [root@exchange-online]# systemctl start taler-exchange.target


.. note::

   At this point, the exchange service is not yet fully operational.


To check whether the exchange is running correctly under the advertised
base URL, run:

.. code-block:: shell-session

  [root@exchange-online]# export BASE_URL=$(taler-config -s exchange -o base_url)
  [root@exchange-online]# wget ${BASE_URL}management/keys


Offline Signing Procedure
=========================

The exchange HTTP service should be running now, but is not yet completely
operational.  To make the exchange HTTP service operational, the following
steps involving the offline signing machine must be completed:

1. The public keys of various online keys used by the exchange service are exported
   via a management HTTP API
2. The offline signing system validates this request and signs it.
   Additionally, the offline signing system signs policy messages
   to configure the exchange's bank accounts and associated fees.
3. The messages generated by the offline signing system are uploaded
   via the management API of the exchange HTTP service.


.. code-block:: shell-session

  [root@exchange-online]# taler-exchange-offline \
    download > sig-request.json

  [root@exchange-offline]# taler-exchange-offline \
    sign < sig-request.json > sig-response.json
  [root@exchange-offline]# taler-exchange-offline \
    enable-account payto://sepa/$IBAN > acct-response.json
  [root@exchange-offline]# taler-exchange-offline \
    wire-fee 2021 sepa EUR:0 EUR:0 > fee-response.json
  [root@exchange-online]# taler-exchange-offline upload < sig-response.json
  [root@exchange-online]# taler-exchange-offline upload < acct-response.json
  [root@exchange-online]# taler-exchange-offline upload < fee-response.json




Testing and Troubleshooting
===========================

The following shell session illustrates how the wallet can be used to withdraw
electronic cash from the exchange and subsequently spend it.  For these steps,
a merchant backend is not required, as the wallet acts as a merchant.


.. code-block:: shell-session

  # This will now output a payto URI that money needs to be sent to in order to allow withdrawal
  # of taler coins
  $ taler-wallet-cli advanced withdraw-manually --exchange $EXCHANGE_URL --amount EUR:10.50

  # Show the status of the manual withdrawal operation
  $ taler-wallet-cli transactions

  #
  # At this point, a bank transfer to the exchange's bank account
  # needs to be made with the correct subject / remittance information
  # as instructed by the wallet after the first step.
  #

  # Check whether the exchange received an incoming bank transfer
  [root@exchange-online]# taler-exchange-wire-gateway-client --section exchange-account-1 --credit-history
  # FIXME: this one above fails, complaining that the section's name doesn't begin with `exchange-accountcredentials-`
  # Blocks also the further steps from being taken.  Should the include in line 33 point inside the "secrets" directory?
  # https://git.taler.net/exchange.git/tree/debian/etc-taler-exchange/taler/conf.d/exchange-business.conf?id=289b816e1cd1a56a0b82582b69bff22c55e6b8a0

  # Once the transfer has been made, try completing the withdrawal
  $ taler-wallet-cli run-pending

  # Check status of transactions and show balance
  $ taler-wallet-cli transactions
  $ taler-wallet-cli balance

  # Now, directly deposit coins with the exchange into a target account
  # (Usually, a payment is made via a merchant.  The wallet provides
  # this functionality for testing.)
  $ taler-wallet-cli deposit create EUR:5 payto://sepa/$IBAN

  # Check if transaction was successful.
  # (If not, fix issue with exchange and run "run-pending" command again)
  $ taler-wallet-cli transactions

  # The wallet can also track if the exchange wired the money to the merchant account.
  # The "deposit group id" can be found in the output of the transactions list.
  $ taler-wallet-cli deposit track $DEPOSIT_GROUP_ID

  # Check whether the exchange sent an outgoing transfer
  [root@exchange-online]# taler-exchangewire-gateway-client --section exchange-account-1 --debit-history

  # After enough time has passed, the money should arrive at the specified IBAN


Summary of Variables
====================

This section summarizes all placeholder variables used in this document.


TBD.


FIXMEs
======

* We should have some summary with the inventory of services that should be
  running.  Systemd by default doesn't show this nicely.  Maybe suggest running
  "systemd list-dependencies taler-exchange.target"?
* When multiple TWGs are configured, which one will be used by the taler-exchange-transfer?
* On Ubuntu focal fossa, I get the following warning on "apt update", are we doing something wrong?

  N: Skipping acquire of configured file 'main/binary-i386/Packages' as
  repository 'https://deb.taler.net/apt/ubuntu focal-fossa InRelease' doesn't
  support architecture 'i386'