View source for Help:Toolforge/My first Flask OAuth tool

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== Overview ==
Python webservices are used by many existing tools. [[W:Python (programming language)|Python]] is a high-level, interpreted programming language with many available libraries for making webservices and integrating with MediaWiki. 

This stub webservice is designed to get a sample Python application installed onto Toolforge as quickly as possible. The application is written using the [[W:Flask (web framework)|Flask framework]].  

'''The guide will teach you how to:'''

* Create a new tool
* Run a Python 3 [[w:Web Server Gateway Interface|WSGI]] webservice on [[Help:Toolforge/Kubernetes|Kubernetes]]
* Allow webservice visitors to authenticate via [[Mw:Help:OAuth|OAuth]] v1 using their [[W:Wikipedia:Unified login|Wikimedia unified account]]

== Getting started ==

=== Prerequisites ===

==== Skills ====

* Basic knowledge of [[W:Python (programming language)|Python]]
* Basic knowledge of [[W:Secure Shell|SSH]]
* Basic knowledge of the [[W:Unix|Unix command line]]
* Familiarity with [[Mw:OAuth/For Developers|OAuth]] (v1) terminology would be nice but not required

==== Accounts ====

* [[Portal:Toolforge/Quickstart|A Toolforge account]]

== Step-by-step guide ==

* Step 1: Create a new tool account
* Step 2: Create a basic Flask WSGI webservice
* Step 3: Add a configuration file
* Step 4: Add support for OAuth1 authentication

=== Step 1: Create a new tool account ===

# Follow the [[Portal:Toolforge/Quickstart|Toolforge quickstart]] guide to create a Toolforge tool and SSH into Toolforge.
#* For the examples in this tutorial, <code>&lt;TOOL NAME&gt;</code> is used to indicate places where your unique tool name is used in another command.
# Run <syntaxhighlight lang="shell-session" inline>$ become <TOOL NAME></syntaxhighlight> to change to the tool user.

=== Step 2: Create a basic Flask WSGI webservice ===

;What is Flask? 

[[W:Flask (web framework)|Flask]] is a popular web development framework for Python.

==== How to create a basic Flask WSGI webservice ====

;Create the $HOME/www/python/src directory for your application:

{{Codesample|lang=shell-session|scheme=light|code=
$ mkdir -p $HOME/www/python/src
}}

;Create a Python virtual environment for the application's external library dependencies

The virtual environment allows the tool to install Python libraries locally without needing a Toolforge administrator's help. The default <code>webservice</code> configuration will automatically load libraries from <code>$HOME/www/python/venv</code>.

The webservice will run on [[W:Kubernetes|Kubernetes]]. A Kubernetes shell is required to create the virtual environment. 

This will ensure that the version of Python the virtual environment uses matches the version of Python used by the Kubernetes runtime.

{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes {{toolforge latest image|python3}} shell
If you don't see a command prompt, try pressing enter.
$ python3 -m venv $HOME/www/python/venv
$ source $HOME/www/python/venv/bin/activate
$ pip install --upgrade pip
Downloading/unpacking pip from [...]
[...]
Successfully installed pip
Cleaning up...
}}

If you run <code>python3 -m venv $HOME/www/python/venv</code> and get an error beginning with "The virtual environment was not created successfully because ensurepip is not available.", you didn't run the first command (the "webservice" one) first.

;Add Flask to the virtual environment

'''Note:''' It is Python best practice to use a file named <code>requirements.txt</code> to keep track of the library dependencies of applications, which can be generated by running <code>pip freeze > requirements.txt</code>.

{{Codesample|lang=shell-session|scheme=light|code=
$ cat > $HOME/www/python/src/requirements.txt << EOF
flask
EOF
$ pip install -r $HOME/www/python/src/requirements.txt
Collecting flask (from -r www/python/src/requirements.txt (line 1))
[...]
Successfully installed [...]
}}

The initial virtual environment is now set-up. Exit out of the Kubernetes shell and return to the SSH session on the bastion.

{{Codesample|lang=shell-session|scheme=light|code=
$ exit
}}

;Create a 'hello world' WSGI application

{{Codesample|lang=shell-session|scheme=light|name=$HOME/www/python/src/app.py|code=
# -*- coding: utf-8 -*-
#
# This file is part of the Toolforge flask WSGI tutorial
#
# Copyright (C) 2017 Bryan Davis and contributors
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# This program 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 General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.

import flask


app = flask.Flask(__name__)


@app.route('/')
def index():
  return 'Hello World!'
}}

'''Note:''' The 'Hello World!' file above starts with a license header that places it under the [https://www.gnu.org/copyleft/gpl.html GPLv3+ license]. 

Code on Toolforge should always be licensed under an [https://opensource.org/licenses Open Source Initiative (OSI) approved license]. See the [[Help:Toolforge/Right to fork policy|Right to fork policy]] for more information on this Toolforge policy.

;Start the webservice

{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes {{toolforge latest image|python3}} start
Starting webservice.
}}
Once the webservice is started, navigate to <code><nowiki>https://</nowiki>&lt;TOOL NAME&gt;.toolforge.org/</code> in your web browser, and see a 'Hello World!' message. It might take a few minutes until it is reachable.

==== Notes ====
Toolforge uses a uWSGI configuration designed to make it easy to deploy a typical Python webservice. This configuration uses a '[[w:Convention over configuration|convention over configuration]]' design with the following expectations:
* The application will have a WSGI entry point in <code>$HOME/www/python/src/app.py</code> in a variable named <code>app</code>.
* Python libraries will be loaded from a virtualenv located in <code>$HOME/www/python/venv</code>.
* Logs will be written to <code>$HOME/uwsgi.log</code>

;Expected file layout
{{Codesample|lang=text|scheme=light|code=
$HOME
 ├─ uwsgi.log
 └─ www
     └─ python
         ├─ src
         │   └─ app.py
         └─ venv
}}

==== Troubleshooting ====

If there is an error when the webservice is started, look in <code>$HOME/uwsgi.log</code> and <code>$HOME/error.log</code> for an explanation. 

One Unix utility to use for this is <code>[https://linux.die.net/man/1/tail tail]</code>, which will display lines from the end of a file:

{{Codesample|lang=shell-session|scheme=light|code=
$ tail -n 50 $HOME/uwsgi.log
$ tail -n 50 $HOME/error.log
}}

=== Step 3: Add a configuration file ===

The application will eventually need some configuration data like OAuth secrets or passwords. These should not be hard coded into the Python files, because the secrets and passwords will be visible once the source code is made public.

There are many different ways to separate code from configuration, but the most straight forward when using Flask is to keep the configuration in a file that can be parsed easily, and then add it to the <code>app.config</code> object that Flask provides.

==== How to add a configuration file ====

;Add PyYAML to the virtual environment

In this tutorial, a YAML file is used to hold secrets. YAML is a nice choice, because it has a simple syntax, is fairly easy for humans to read, and supports both comments and complex values like lists and dictionaries. 

Python does not have built in support for parsing YAML files. Install a library to help out.

{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes {{toolforge latest image|python3}} shell
If you don't see a command prompt, try pressing enter.
$ source $HOME/www/python/venv/bin/activate
$ cat >> $HOME/www/python/src/requirements.txt << EOF
pyyaml
EOF
$ pip install -r $HOME/www/python/src/requirements.txt
Requirement already satisfied: flask [...]
Collecting pyyaml (from -r req.txt (line 2))
[...]
Successfully installed pyyaml
$ exit
}}

;Read configuration from a file

Update the <code>$HOME/www/python/src/app.py</code> file to read configuration from a <code>config.yaml</code> file in the same directory and get the greeting from the configuration file:

{{Codesample|lang=python3|scheme=light|name=$HOME/www/python/src/app.py|code=
# -*- coding: utf-8 -*-
#
# This file is part of the Toolforge Flask + OAuth WSGI tutorial
#
# Copyright (C) 2017 Bryan Davis and contributors
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# This program 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 General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.

import flask
import os
import yaml


app = flask.Flask(__name__)


# Load configuration from YAML file
__dir__ = os.path.dirname(__file__)
app.config.update(
    yaml.safe_load(open(os.path.join(__dir__, 'config.yaml'))))


@app.route('/')
def index():
    return app.config['GREETING']
}}

A configuration file is now required or the application will produce an error. Eventually, secrets will be included in this file. The file's permissions should be changed so that only the tool user can read it.

{{Codesample|lang=shell-session|scheme=light|code=
$ touch $HOME/www/python/src/config.yaml
$ chmod u=rw,go= $HOME/www/python/src/config.yaml
$ cat > $HOME/www/python/src/config.yaml << EOF
GREETING: Goodnight moon!
EOF
}}
Now restart the webservice:
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice restart
Restarting webservice...
}}

Once the webservice has restarted, navigate to <code><nowiki>https://</nowiki>&lt;TOOL NAME&gt;.toolforge.org/</code> in your web browser and see the new 'Goodnight moon!' message.

==== Troubleshooting ====

If there is an error, look in <code>$HOME/uwsgi.log</code> and <code>$HOME/error.log</code> for an explanation.

=== Step 4: Add support for OAuth authentication ===

OAuth is a safe mechanism for authenticating a Wikimedia user in the application. For the basics, [[Mw:OAuth/For Developers|read more about OAuth on mediawiki.org]].

==== How to add mwoauth to the virtual environment ====

[https://pythonhosted.org/mwoauth/ mwoauth library] is used to handle most of the complexity of making OAuth requests to MediaWiki.

{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes {{toolforge latest image|python3}} shell
If you don't see a command prompt, try pressing enter.
$ source $HOME/www/python/venv/bin/activate
$ cat >> $HOME/www/python/src/requirements.txt << EOF
mwoauth
EOF
$ pip install -r $HOME/www/python/src/requirements.txt
Requirement already satisfied: flask [...]
Requirement already satisfied: pyyaml [...]
Collecting mwoauth (from -r req.txt (line 3))
[...]
Successfully installed [...]
$ exit
}}

;Update the application code
Here is our new <code>$HOME/www/python/src/app.py</code> file:
{{Collapse top|www/python/src/app.py}}
{{Codesample|lang=python3|scheme=light|name=$HOME/www/python/src/app.py|code=
# -*- coding: utf-8 -*-
#
# This file is part of the Toolforge Flask + OAuth WSGI tutorial
#
# Copyright (C) 2017 Bryan Davis and contributors
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# This program 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 General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.

import flask
import mwoauth
import os
import yaml


app = flask.Flask(__name__)


# Load configuration from YAML file
__dir__ = os.path.dirname(__file__)
app.config.update(
    yaml.safe_load(open(os.path.join(__dir__, 'config.yaml'))))


@app.route('/')
def index():
    greeting = app.config['GREETING']
    username = flask.session.get('username', None)
    return flask.render_template(
        'index.html', username=username, greeting=greeting)


@app.route('/login')
def login():
    """Initiate an OAuth login.
    
    Call the MediaWiki server to get request secrets and then redirect the
    user to the MediaWiki server to sign the request.
    """
    consumer_token = mwoauth.ConsumerToken(
        app.config['CONSUMER_KEY'], app.config['CONSUMER_SECRET'])
    try:
        redirect, request_token = mwoauth.initiate(
            app.config['OAUTH_MWURI'], consumer_token)
    except Exception:
        app.logger.exception('mwoauth.initiate failed')
        return flask.redirect(flask.url_for('index'))
    else:
        flask.session['request_token'] = dict(zip(
            request_token._fields, request_token))
        return flask.redirect(redirect)


@app.route('/oauth-callback')
def oauth_callback():
    """OAuth handshake callback."""
    if 'request_token' not in flask.session:
        flask.flash(u'OAuth callback failed. Are cookies disabled?')
        return flask.redirect(flask.url_for('index'))

    consumer_token = mwoauth.ConsumerToken(
        app.config['CONSUMER_KEY'], app.config['CONSUMER_SECRET'])

    try:
        access_token = mwoauth.complete(
            app.config['OAUTH_MWURI'],
            consumer_token,
            mwoauth.RequestToken(**flask.session['request_token']),
            flask.request.query_string)

        identity = mwoauth.identify(
            app.config['OAUTH_MWURI'], consumer_token, access_token)    
    except Exception:
        app.logger.exception('OAuth authentication failed')
    
    else:
        flask.session['access_token'] = dict(zip(
            access_token._fields, access_token))
        flask.session['username'] = identity['username']

    return flask.redirect(flask.url_for('index'))


@app.route('/logout')
def logout():
    """Log the user out by clearing their session."""
    flask.session.clear()
    return flask.redirect(flask.url_for('index'))
}}
{{Collapse bottom}}

The new <code>app.py</code> uses the Jinja template system that is built into Flask rather than the bare strings that were used in the 'hello world' version. One reason for this is that Jinja will automatically escape strings. This is important in any application that will be serving data gathered from a user or even a database to protect against security vulnerabilities like [[w:Cross-site scripting|cross-site scripting]]. 

By default Flask will look for templates in the <code>$HOME/www/python/src/templates</code> directory.
{{Codesample|lang=shell-session|scheme=light|code=
$ mkdir $HOME/www/python/src/templates
$ edit $HOME/www/python/src/templates/index.html
}}
{{Codesample|lang=html+jinja|scheme=light|name=$HOME/www/python/src/templates/index.html|code=
<!DOCTYPE HTML>
<html>
    <head>
        <title>My first Flask OAuth tool</title>
    </head>
    <body>
        {% if username %}
        <p>Hello {{((}} username {{))}}!</p>
        <p><a href="{{((}} url_for('logout') {{))}}">logout</a></p>
        {% else %}
        <p>{{((}} greeting {{))}}</p>
        <p><a href="{{((}} url_for('login') {{))}}">login</a></p>
        {% endif %}
    </body>
</html>
}}

;Update the configuration to add OAuth secrets

Add new configuration values to <code>$HOME/www/python/src/config.yaml</code> file to go with the new code.

# [https://meta.wikimedia.org/wiki/Special:OAuthConsumerRegistration/propose Register a new OAuth consumer]. 
# As callback URL, use: <code><nowiki>https://</nowiki>&lt;TOOL NAME&gt;.toolforge.org/oauth-callback</code>
# As contact e-mail address, use the e-mail address linked to your Wikimedia unified account.
# Keep the default grant settings ('Request authorization for specific permissions.' with just 'Basic rights' selected)
#:* You will be able to use your own account before the consumer has been approved.
# Copy the ''consumer token'' and ''secret token'' values that are generated. These are needed for the config.yaml file.

{{Codesample
| lang = shell-session
| scheme = light
| code = $ cat >> $HOME/www/python/src/config.yaml << EOF
SECRET_KEY: $(python3 -c "import secrets; print(secrets.token_urlsafe(48))")
OAUTH_MWURI: https://meta.wikimedia.org/w/index.php
CONSUMER_KEY: the 'consumer token' value from your OAuth consumer registration
CONSUMER_SECRET: the 'secret token' value from your OAuth consumer registration
EOF
}}

;Restart the webservice
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice restart
Restarting webservice...
}}
Once the webservice has restarted, navigate to <code><nowiki>https://</nowiki>&lt;TOOL NAME&gt;.toolforge.org/</code> in your web browser to see the new landing page.

Try using the ''login'' and ''logout'' links to test out the OAuth integration.

== Additional troubleshooting ==

=== bash: webservice: command not found ===

# Check shell prompt. 
# If it ends in <code>@interactive $</code>, you are inside a Kubernetes shell (<code>webservice --backend=kubernetes {{toolforge latest image|python3}} shell</code>). 
#:* The <code>webservice</code> command is only available on the Toolforge bastions. 
# Type <code>exit</code> to leave the Kubernetes shell and return to the bastion.

=== Error: An error occurred in the OAuth protocol: Invalid signature ===

# Double check the values set for <code>CONSUMER_KEY</code> and <code>CONSUMER_SECRET</code>

=== Get more debugging output from Flask ===

# Add <code>Debug: True</code> to <code>config.yaml</code> 
# Check <code>uwsgi.log</code> for more information. 
'''Note:''' This needs a <code>webservice restart</code> to take effect.

=== toolsws.tool.InvalidToolException: Tool username should begin with tools. ===

# Run <code>become &lt;TOOL NAME&gt;</code> to change to the tool user.

== Next Steps ==

Now that your Flask OAuth tool is set-up here are some next steps to consider:

* Use the OAuth token data stored in <code>flask.session['access_token']</code> to make [[Mw:API:Main page|API calls]] as the authorized user. 
* Explore the [https://pypi.python.org/pypi/mwclient mwclient] library to make interacting with the MediaWiki Action API easier.
* [[Help:Toolforge#Setting up code review and version control|Publish your source code in a git repository]].
* Add a co-maintainer.
* [[:Category:Toolforge tools|Create a description page for your tool]].
* Use the [[User:Legoktm/toolforge library|toolforge library]] to set a nice user agent.
* If possible, run the tool on your local system as well (clone the source code repository, install dependencies, run <code>FLASK_APP=app.py FLASK_ENV=development flask run</code>). In development mode (which you should never run on Toolforge!), Flask offers some additional conveniences, such as automatic reloading of source files on save or an in-browser debugger on errors.

{{:Help:Cloud Services communication}}

== See also ==

* [[Phab:source/tool-my-first-flask-oauth-tool/|Git repository 'tool-my-first-flask-oauth-tool' on Phabricator]]
* [[toolforge:my-first-flask-oauth-tool/|My-first-flask-oauth-tool on Toolforge]]
* [[Help:Toolforge/My first Django OAuth tool]]
* [[Help:Toolforge/My first NodeJS OAuth tool]]

[[Category:Toolforge|Flask]]
[[Category:Documentation|Toolforge]]