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{{Toolforge nav}}
{{Toolforge nav}}


'''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 the tools-project as quickly as possible. The application is written using the [[W:Flask (web framework)|flask framework]]. 
== 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 guide assumes you have [[Help:Toolforge/Getting started|a Toolforge account]] and basic knowledge of Python, [[W:Secure Shell|SSH]] and the UNIX command line.  
This stub webservice is designed to get a sample Python application installed onto the tools-project as quickly as possible. The application is written using the [[W:Flask (web framework)|Flask framework]].


The goal of this guide is to:
'''The guide will teach you how to:'''


* Create a new tool
* Create a new tool
* Run a Python 3 [[W:Web Server Gateway Interface|WSGI]] webservice on [[Help:Toolforge/Web/Kubernetes|Kubernetes]]
* Run a Python 3 [[W:Web Server Gateway Interface|WSGI]] webservice on [[Help:Toolforge/Web/Kubernetes|Kubernetes]]
* Allow webservice visitors to authenticate via [[Mw:Help:OAuth|OAuth]] using their [[W:Wikipedia:Unified login|Wikimedia unified account]]
* Allow webservice visitors to authenticate via [[Mw:Help:OAuth|OAuth]] 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]]
* Basic knowledge of [[W:Kubernetes|Kubernetes]]
* Basic knowledge of [[Mw:OAuth/For Developers| OAuth]]
==== Accounts ====
* [[Help:Toolforge/Getting started|A Toolforge account]]
== Steps to completion ==
* Create a new tool account
* Create a basic Flask WSGI webservice
* Add a configuration file
* Add support for OAuth authentication
== Step-by-step guide ==


== Step 1: Create a new tool account ==
== Step 1: Create a new tool account ==
A '''tool account''' (also known as a 'service group') is a shared UNIX account intended to host and run application code in Toolforge. A tool account can have multiple Toolforge members with 'maintainer' access which allows users to collaborate on building and running the tool.
 
=== What is a tool account? ===
 
A '''tool account''' (also known as a 'service group') is a shared UNIX account intended to host and run application code in Toolforge.  
 
A tool account can have multiple Toolforge members with 'maintainer' access, which allows users to collaborate together to build and run the tool.
 
=== How to create a new tool account ===
 
* Create a [https://toolsadmin.wikimedia.org/tools/ new tool] with a unique name. This name will be part of the URL for the final webservice.[[File:Screenshot about creating a new tool..png|thumb]]
* Create a [https://toolsadmin.wikimedia.org/tools/ new tool] with a unique name. This name will be part of the URL for the final webservice.[[File:Screenshot about creating a new tool..png|thumb]]
** In this tutorial, we use <code>&lt;TOOL NAME&gt;</code> everywhere the tool name should be used in another command.
** In this tutorial, we use <code>&lt;TOOL NAME&gt;</code> everywhere the tool name should be used in another command.  
** <code>&lt;TOOL NAME&gt;</code> must start with a-z, end with a-z or 0-9, be 1-32 characters long, and can only contain lowercase a-z, 0-9, and - characters.  
* SSH to login.tools.wmflabs.org.
* SSH to login.tools.wmflabs.org.
** If you are already logged in, log out and log in again so that your session will see that you have been added to a new tool account.
 
** If the local and remote username are different. SSH to <shell_username>@login.tools.wmflabs.org.  
=== Notes ===
 
* <code>&lt;TOOL NAME&gt;</code> must start with a-z, end with a-z or 0-9, be 1-32 characters long, and can only contain lowercase a-z, 0-9, and - characters.
* If you are already logged in, log out and log in again. Your session will see that you have been added to a new tool account.
* If the local and remote username are different. SSH to <shell_username>@login.tools.wmflabs.org.  
* Run <code>become &lt;TOOL NAME&gt;</code> to change to the tool user.
* Run <code>become &lt;TOOL NAME&gt;</code> to change to the tool user.
** It may take a while for the new tool's home directory and files to get created. If you get an error message like <code>become: no such tool '<TOOL NAME>'</code> wait a few minutes and try again.
 
** If you get an error message like <code>You are not a member of the group <TOOL NAME></code> try logging out and logging back in again so that your session will see that you have been added to a new tool account.
=== Troubleshooting ===
 
* It may take a while for the new tool's home directory and files to get created. If you get an error message like <code>become: no such tool '<TOOL NAME>'</code> wait a few minutes, and try again.
* If you get an error message like <code>You are not a member of the group <TOOL NAME></code> try logging out and logging back in again, so that your session will see that you have been added to a new tool account.


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


Toolforge has an opinionated default configuration for running WSGI applications. The configuration expects a Python virtual environment in <code>$HOME/www/python/venv</code> and the WSGI application entry point to be named <code>app</code> and loaded from<code>$HOME/www/python/src/app.py</code>. Changing these locations is possible, but outside the scope of this tutorial. Generally it is easier to make your tool conform to the Toolforge expectations than to work around them.
=== What is Flask? ===


'''Expected file layout'''<syntaxhighlight lang="shell">
[[W:Flask (web framework)|Flask]] is a popular web development framework for Python.
$HOME
 
└── www
=== How to create a basic Flask WSGI webservice ===
    └── python
        ├── src
        │  └── app.py
        └── venv
</syntaxhighlight>


=== Create the $HOME/www/python/src directory for your application ===
==== Create the $HOME/www/python/src directory for your application ====
<syntaxhighlight lang="shell-session">
<syntaxhighlight lang="shell-session">
$ mkdir -p $HOME/www/python/src
$ mkdir -p $HOME/www/python/src
</syntaxhighlight>
</syntaxhighlight>


=== Create a Python virtual environment for the application's external library dependencies ===
==== Create a Python virtual environment for the application's external library dependencies ====
The virtual environment will allow your 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>$HOME/www/python/venv</code>.
The virtual environment will allow your tool to install Python libraries locally without needing a Toolforge administrator's help. The default <code>webservice</code> configuration will automatically load libraries from <code>$HOME/www/python/venv</code>.


We are going to run our webservice on Kubernetes, so we will need to use a Kubernetes shell to create our virtual environment. This will ensure that the version of Python that the virtual environment uses matches the version of Python used by the Kubernetes runtime.<syntaxhighlight lang="shell-session">
The webservice will run on [[W:Kubernetes|Kubernetes]], so we will need to use a Kubernetes shell to create our virtual environment.  
 
This will ensure that the version of Python that the virtual environment uses matches the version of Python used by the Kubernetes runtime.
 
<syntaxhighlight lang="shell-session">
$ webservice --backend=kubernetes python shell
$ webservice --backend=kubernetes python shell
If you don't see a command prompt, try pressing enter.
If you don't see a command prompt, try pressing enter.
Line 56: Line 95:
</syntaxhighlight>
</syntaxhighlight>


=== Add flask to the virtual environment ===
==== Add Flask to the virtual environment ====
Using a file named requirements.txt to keep track of the library dependencies of your application is a Python best practice.<syntaxhighlight lang="shell-session">
 
'''Note:''' It is Python best practice to use a file named <code>requirements.txt</code> to keep track of the library dependencies of your application.
 
<syntaxhighlight lang="shell-session">
$ cat > $HOME/www/python/src/requirements.txt << EOF
$ cat > $HOME/www/python/src/requirements.txt << EOF
flask
flask
Line 65: Line 107:
[...]
[...]
Successfully installed [...]
Successfully installed [...]
</syntaxhighlight>We are done setting up the initial virtual environment, so exit out of the Kubernetes shell and return to your SSH session on the bastion.<syntaxhighlight lang="shell-session">
</syntaxhighlight>
 
The initial virtual environment is now set-up. Exit out of the Kubernetes shell and return to your SSH session on the bastion.
 
<syntaxhighlight lang="shell-session">
$ exit
$ exit
</syntaxhighlight>
</syntaxhighlight>


=== Create a 'hello world' WSGI application ===
==== Create a 'hello world' WSGI application ====
Lets make sure that all of the basics are working by creating a very simple 'hello world' WSGI app and running it. The default <code>webservice</code> configuration will look for an <code>app</code> variable in <code>$HOME/www/python/src/app.py</code> as the main WSGI application entry point. Create your <code>$HOME/www/python/src/app.py</code> file with these contents:<syntaxhighlight lang="python">
<syntaxhighlight lang="python3">
# -*- coding: utf-8 -*-
# -*- coding: utf-8 -*-
#
#
Line 99: Line 145:
def index():
def index():
   return 'Hello World!'
   return 'Hello World!'
</syntaxhighlight>This file starts with a license header placing 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 the Toolforge policy.
</syntaxhighlight>
 
This file starts with a license header placing it under the [https://www.gnu.org/copyleft/gpl.html GPLv3+ license].  
 
'''Note:''' 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 the Toolforge policy.


=== Start the webservice ===
==== Start the webservice ====
<syntaxhighlight lang="shell-session">
<syntaxhighlight lang="shell-session">
$ webservice --backend=kubernetes python start
$ webservice --backend=kubernetes python start
Line 108: Line 158:
Once the webservice is started, you should be able to go to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser and see a cheery 'Hello World!' message.
Once the webservice is started, you should be able to go to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser and see a cheery 'Hello World!' message.


If you see an error instead, look in <code>$HOME/uwsgi.log</code> and <code>$HOME/error.log</code> for an explanation. One unix utility to do that is <code>[https://linux.die.net/man/1/tail tail]</code> which will display lines from the end of a file:
=== Notes ===
 
Toolforge uses a strict default configuration for running WSGI applications. The configuration expects a Python virtual environment in <code>$HOME/www/python/venv</code> and the WSGI application entry point to be named <code>app</code> and loaded from<code>$HOME/www/python/src/app.py</code>.
 
'''Expected file layout'''<syntaxhighlight lang="shell">
$HOME
└── www
    └── python
        ├── src
        │  └── app.py
        └── venv
</syntaxhighlight>
 
=== Troubleshooting ===
 
If you see an error when you start the webservice, look in <code>$HOME/uwsgi.log</code> and <code>$HOME/error.log</code> for an explanation.  
'''Note:''' One Unix utility to do that is <code>[https://linux.die.net/man/1/tail tail]</code> which will display lines from the end of a file:
<syntaxhighlight lang="shell-session">
<syntaxhighlight lang="shell-session">
$ tail -n 50 $HOME/uwsgi.log
$ tail -n 50 $HOME/uwsgi.log
Line 115: Line 181:


== Step 3: Add a configuration file ==
== Step 3: Add a configuration file ==
Our application will eventually need some configuration data like OAuth secrets or passwords. These should not be hard coded into the Python files directly because that will make it impossible for us to publish our source code publicly without exposing those secrets.


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


=== Add PyYAML to the virtual environment ===
In this tutorial, we will use a YAML file to hold our 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.  
In this tutorial we will use a YAML file to hold our 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, so we will install a library to help out.<syntaxhighlight lang="shell-session">
 
Python does not have built in support for parsing YAML files, so we will install a library to help out.
 
<syntaxhighlight lang="shell-session">
$ webservice --backend=kubernetes python shell
$ webservice --backend=kubernetes python shell
If you don't see a command prompt, try pressing enter.
If you don't see a command prompt, try pressing enter.
Line 135: Line 209:
</syntaxhighlight>
</syntaxhighlight>


=== Read configuration from a file ===
==== Read configuration from a file ====
Update our <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:<syntaxhighlight lang="python">
 
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:
 
<syntaxhighlight lang="python">
# -*- coding: utf-8 -*-
# -*- coding: utf-8 -*-
#
#
Line 173: Line 250:
def index():
def index():
     return app.config['GREETING']
     return app.config['GREETING']
</syntaxhighlight>We need a configuration file now or our application will have an error when it tries to read it. We are eventually going to put secrets in this file too, so we need to change the file's permissions so that only our tool user can read it.<syntaxhighlight lang="shell-session">
</syntaxhighlight>
 
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.
 
<syntaxhighlight lang="shell-session">
$ touch $HOME/www/python/src/config.yaml
$ touch $HOME/www/python/src/config.yaml
$ chmod u=rw,go= $HOME/www/python/src/config.yaml
$ chmod u=rw,go= $HOME/www/python/src/config.yaml
Line 183: Line 264:
Restarting webservice...
Restarting webservice...
</syntaxhighlight>Once the webservice has restarted, you should be able to go to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser and see the new 'Goodnight moon!' message.
</syntaxhighlight>Once the webservice has restarted, you should be able to go to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser and see the new 'Goodnight moon!' message.
==== Troubleshooting ====


If you see an error instead, look in <code>$HOME/uwsgi.log</code> and <code>$HOME/error.log</code> for an explanation.
If you see an error instead, look in <code>$HOME/uwsgi.log</code> and <code>$HOME/error.log</code> for an explanation.
Line 188: Line 271:
== Step 4: Add support for OAuth authentication ==
== Step 4: Add support for OAuth authentication ==


OAuth is a safe mechanism for authenticating a Wikimedia user in your application. Explaining how OAuth works and all of the things that a developer should be aware of is out of scope for this tutorial. [[Mw:OAuth/For Developers|Read more about OAuth on mediawiki.org]] if you are unfamiliar with the basics.
OAuth is a safe mechanism for authenticating a Wikimedia user in your application. If you are unfamiliar with the basics, [[Mw:OAuth/For Developers|read more about OAuth on mediawiki.org]].


=== Add mwoauth to the virtual environment ===
=== How to add mwoauth to the virtual environment ===
We are going to use the [https://pythonhosted.org/mwoauth/ mwoauth library] to handle most of the complexity of making OAuth requests to MediaWiki.<syntaxhighlight lang="shell-session">
 
[https://pythonhosted.org/mwoauth/ mwoauth library] is used to handle most of the complexity of making OAuth requests to MediaWiki.
 
<syntaxhighlight lang="shell-session">
$ webservice --backend=kubernetes python shell
$ webservice --backend=kubernetes python shell
If you don't see a command prompt, try pressing enter.
If you don't see a command prompt, try pressing enter.
Line 207: Line 293:
</syntaxhighlight>
</syntaxhighlight>


=== Update the application code ===
==== Update the application code ====
Here is our new <code>$HOME/www/python/src/app.py</code> file:
Here is our new <code>$HOME/www/python/src/app.py</code> file:
{{Collapse top|www/python/src/app.py}}
{{Collapse top|www/python/src/app.py}}
Line 256: Line 342:
def login():
def login():
     """Initiate an OAuth login.
     """Initiate an OAuth login.
   
     Call the MediaWiki server to get request secrets and then redirect the
     Call the MediaWiki server to get request secrets and then redirect the
     user to the MediaWiki server to sign the request.
     user to the MediaWiki server to sign the request.
Line 292: Line 378:


         identity = mwoauth.identify(
         identity = mwoauth.identify(
             app.config['OAUTH_MWURI'], consumer_token, access_token)
             app.config['OAUTH_MWURI'], consumer_token, access_token)  
     except Exception:
     except Exception:
         app.logger.exception('OAuth authentication failed')
         app.logger.exception('OAuth authentication failed')
   
     else:
     else:
         flask.session['access_token'] = dict(zip(
         flask.session['access_token'] = dict(zip(
Line 312: Line 398:
{{Collapse bottom}}
{{Collapse bottom}}


The new <code>app.py</code> uses the Jinja template system that is built into Flask rather than the bare strings that we used in the 'hello world' version. One reason for this is that Jinja will automatically escape strings for us. 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 your <code>$HOME/www/python/src/templates</code> directory.
The new <code>app.py</code> uses the Jinja template system that is built into Flask rather than the bare strings that we 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.
<syntaxhighlight lang="shell-session">
<syntaxhighlight lang="shell-session">
$ mkdir $HOME/www/python/src/templates
$ mkdir $HOME/www/python/src/templates
Line 334: Line 422:
</syntaxhighlight>
</syntaxhighlight>


=== Update the configuration to add OAuth secrets ===
==== Update the configuration to add OAuth secrets ====
We are going to need to add some new configuration values to our <code>$HOME/www/python/src/config.yaml</code> file to go with the new code.  
 
==== Add new configuration values to <code>$HOME/www/python/src/config.yaml</code> file to go with the new code.====


First we need to [https://meta.wikimedia.org/wiki/Special:OAuthConsumerRegistration/propose register a new OAuth consumer]. That will give us two of the new configuration values we need:
# [https://meta.wikimedia.org/wiki/Special:OAuthConsumerRegistration/propose Register a new OAuth consumer].  
* As callback URL, use: <code><nowiki>https://tools.wmflabs.org/</nowiki>&lt;TOOL NAME&gt;/oauth-callback</code>
# As callback URL, use: <code><nowiki>https://tools.wmflabs.org/</nowiki>&lt;TOOL NAME&gt;/oauth-callback</code>
* As contact e-mail address, use the e-mail address linked to your Wikimedia unified account.
# 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)
# Keep the default grant settings ('Request authorization for specific permissions.' with just 'Basic rights' selected)
* Don't worry about approval for now; you can use your own account before the consumer has been approved.
#:* Don't worry about approval for now; you can use your own account before the consumer has been approved.
* Copy the ''consumer token'' and ''secret token'' values that are generated. You will need them for your config.yaml file.
# Copy the ''consumer token'' and ''secret token'' values that are generated. You will need them for your config.yaml file.


<syntaxhighlight lang="shell-session">
<syntaxhighlight lang="shell-session">
Line 353: Line 442:
</syntaxhighlight>
</syntaxhighlight>


Now restart the webservice:<syntaxhighlight lang="shell-session">
==== Restart the webservice====
<syntaxhighlight lang="shell-session">  
$ webservice restart
$ webservice restart
Restarting webservice...
Restarting webservice...
</syntaxhighlight>Once the webservice has restarted, you should be able to go to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser and see the new landing page. Try using the ''login'' and ''logout'' links to test out your OAuth integration.
</syntaxhighlight>Once the webservice has restarted, you should be able to go to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser and see the new landing page. Try using the ''login'' and ''logout'' links to test out your OAuth integration.


== What next? ==
== Additional troubleshooting ==
This application is a starting point, but really doesn't do anything interesting yet. The next logical step would be to 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. You may want to look into [https://pypi.python.org/pypi/mwclient mwclient] library to make interacting with the MediaWiki Action API easier.
 
Other recommended steps to make your tool compliant with Toolforge policies and easier to maintain:
* [[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]]


== Problems? ==
=== bash: webservice: command not found ===
=== bash: webservice: command not found ===
Check to see if your shell prompt ends in <code>@interactive $</code>. If it does, you are inside a Kubernetes shell (<code>webservice --backend=kubernetes python 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.
# Check shell prompt.
# If it ends in <code>@interactive $</code>, you are inside a Kubernetes shell (<code>webservice --backend=kubernetes python 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 ===
=== Error: An error occurred in the OAuth protocol: Invalid signature ===
Double check the values you set for <code>CONSUMER_KEY</code> and <code>CONSUMER_SECRET</code>
# Double check the values you set for <code>CONSUMER_KEY</code> and <code>CONSUMER_SECRET</code>


=== Get more debugging output from Flask ===
=== Get more debugging output from Flask ===
Add <code>Debug: True</code> to <code>config.yaml</code> and check <code>uwsgi.log</code> for more information. Note that this needs a <code>webservice restart</code> to take effect.
# 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.
 
== 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]]


== See also ==
== See also ==

Revision as of 23:42, 25 October 2017

Overview

Python webservices are used by many existing tools. 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 the tools-project as quickly as possible. The application is written using the Flask framework.

The guide will teach you how to:

Getting started

Prerequisites

Skills

Accounts

Steps to completion

  • Create a new tool account
  • Create a basic Flask WSGI webservice
  • Add a configuration file
  • Add support for OAuth authentication

Step-by-step guide

Step 1: Create a new tool account

What is a tool account?

A tool account (also known as a 'service group') is a shared UNIX account intended to host and run application code in Toolforge.

A tool account can have multiple Toolforge members with 'maintainer' access, which allows users to collaborate together to build and run the tool.

How to create a new tool account

  • Create a new tool with a unique name. This name will be part of the URL for the final webservice.
    Screenshot about creating a new tool..png
    • In this tutorial, we use <TOOL NAME> everywhere the tool name should be used in another command.
  • SSH to login.tools.wmflabs.org.

Notes

  • <TOOL NAME> must start with a-z, end with a-z or 0-9, be 1-32 characters long, and can only contain lowercase a-z, 0-9, and - characters.
  • If you are already logged in, log out and log in again. Your session will see that you have been added to a new tool account.
  • If the local and remote username are different. SSH to <shell_username>@login.tools.wmflabs.org.
  • Run become <TOOL NAME> to change to the tool user.

Troubleshooting

  • It may take a while for the new tool's home directory and files to get created. If you get an error message like become: no such tool '<TOOL NAME>' wait a few minutes, and try again.
  • If you get an error message like You are not a member of the group <TOOL NAME> try logging out and logging back in again, so that your session will see that you have been added to a new tool account.

Step 2: Create a basic Flask WSGI webservice

What is Flask?

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

$ mkdir -p $HOME/www/python/src

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

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

The webservice will run on Kubernetes, so we will need to use a Kubernetes shell to create our virtual environment.

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

$ webservice --backend=kubernetes python 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...

Add Flask to the virtual environment

Note: It is Python best practice to use a file named requirements.txt to keep track of the library dependencies of your application.

$ 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 your SSH session on the bastion.

$ exit

Create a 'hello world' WSGI application

# -*- 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!'

This file starts with a license header placing it under the GPLv3+ license.

Note: Code on Toolforge should always be licensed under an Open Source Initiative (OSI) approved license. See the Right to fork policy for more information on the Toolforge policy.

Start the webservice

$ webservice --backend=kubernetes python start
Starting webservice.

Once the webservice is started, you should be able to go to https://tools.wmflabs.org/<TOOL NAME>/ in your web browser and see a cheery 'Hello World!' message.

Notes

Toolforge uses a strict default configuration for running WSGI applications. The configuration expects a Python virtual environment in $HOME/www/python/venv and the WSGI application entry point to be named app and loaded from$HOME/www/python/src/app.py.

Expected file layout

$HOME
└── www
    └── python
        ├── src
        │   └── app.py
        └── venv

Troubleshooting

If you see an error when you start the webservice, look in $HOME/uwsgi.log and $HOME/error.log for an explanation. Note: One Unix utility to do that is tail which will display lines from the end of a file:

$ tail -n 50 $HOME/uwsgi.log
$ tail -n 50 $HOME/error.log

Step 3: Add a configuration file

Your 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 app.config object that Flask provides.

How to add a configuration file

Add PyYAML to the virtual environment

In this tutorial, we will use a YAML file to hold our 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, so we will install a library to help out.

$ webservice --backend=kubernetes python 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 $HOME/www/python/src/app.py file to read configuration from a config.yaml file in the same directory and get the greeting from the configuration file:

# -*- 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.

$ 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:

$ webservice restart
Restarting webservice...

Once the webservice has restarted, you should be able to go to https://tools.wmflabs.org/<TOOL NAME>/ in your web browser and see the new 'Goodnight moon!' message.

Troubleshooting

If you see an error instead, look in $HOME/uwsgi.log and $HOME/error.log for an explanation.

Step 4: Add support for OAuth authentication

OAuth is a safe mechanism for authenticating a Wikimedia user in your application. If you are unfamiliar with the basics, read more about OAuth on mediawiki.org.

How to add mwoauth to the virtual environment

mwoauth library is used to handle most of the complexity of making OAuth requests to MediaWiki.

$ webservice --backend=kubernetes python 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 $HOME/www/python/src/app.py file:

The new app.py uses the Jinja template system that is built into Flask rather than the bare strings that we 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 cross-site scripting.

By default Flask will look for templates in the $HOME/www/python/src/templates directory.

$ mkdir $HOME/www/python/src/templates
$ edit $HOME/www/python/src/templates/index.html
<!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 $HOME/www/python/src/config.yaml file to go with the new code.

  1. Register a new OAuth consumer.
  2. As callback URL, use: https://tools.wmflabs.org/<TOOL NAME>/oauth-callback
  3. As contact e-mail address, use the e-mail address linked to your Wikimedia unified account.
  4. Keep the default grant settings ('Request authorization for specific permissions.' with just 'Basic rights' selected)
    • Don't worry about approval for now; you can use your own account before the consumer has been approved.
  5. Copy the consumer token and secret token values that are generated. You will need them for your config.yaml file.
$ cat >> $HOME/www/python/src/config.yaml << EOF
SECRET_KEY: $(python -c "import os; print repr(os.urandom(24))")
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

 
$ webservice restart
Restarting webservice...

Once the webservice has restarted, you should be able to go to https://tools.wmflabs.org/<TOOL NAME>/ in your web browser and see the new landing page. Try using the login and logout links to test out your OAuth integration.

Additional troubleshooting

bash: webservice: command not found

  1. Check shell prompt.
  2. If it ends in @interactive $, you are inside a Kubernetes shell (webservice --backend=kubernetes python shell).
    • The webservice command is only available on the Toolforge bastions.
  3. Type exit to leave the Kubernetes shell and return to the bastion.

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

  1. Double check the values you set for CONSUMER_KEY and CONSUMER_SECRET

Get more debugging output from Flask

  1. Add Debug: True to config.yaml
  2. Check uwsgi.log for more information.

Note: This needs a webservice restart to take effect.

Next Steps

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

See also