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imported>Ladsgroup
(This wasted hours of my time debugging why the sessions don't stick)
 
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{{Toolforge nav}}
{{Toolforge nav}}
{{TOC|align=right|width=30em}}


== Overview ==
== Overview ==
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* [[Help:Getting Started|A Toolforge account]]
* [[Help:Getting Started|A Toolforge account]]


== Steps to completion ==
== Step-by-step guide ==


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


== Step-by-step guide ==
=== Step 1: Create a new tool account ===


== Step 1: Create a new tool account ==
# Create [[Portal:Toolforge/Tool Accounts#Create tools with Tool Accounts|a new tool account]].
 
# Create [[Help:Toolforge#Tool_Accounts|a new tool account]].
#* 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.
#* 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.
# SSH to login.tools.wmflabs.org.
# SSH to login.toolforge.org.
#* If your local username is different from your shell account name on Toolforge, you will need to include your Toolforge shell account name in your ssh command (i.e. &lt;shell_username&gt;@login.tools.wmflabs.org). See [[Help:Access]] for more information on using SSH.
#* If your local username is different from your shell account name on Toolforge, you will need to include your Toolforge shell account name in your ssh command (i.e. &lt;shell_username&gt;@login.toolforge.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.


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


=== What is Flask? ===
;What is Flask?  


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


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


==== Create the $HOME/www/python/src directory for your application ====
;Create the $HOME/www/python/src directory for your application:
<syntaxhighlight lang="shell-session">
 
{{Codesample|lang=shell-session|scheme=light|code=
$ mkdir -p $HOME/www/python/src
$ mkdir -p $HOME/www/python/src
</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 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>$HOME/www/python/venv</code>.
The virtual environment allows the tool to install Python libraries locally without needing a Toolforge administrator's help. The default <code>webservice</code> configuration will automatically load libraries from <code>$HOME/www/python/venv</code>.


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


<syntaxhighlight lang="shell-session">
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes python shell
$ webservice --backend=kubernetes python3.7 shell
If you don't see a command prompt, try pressing enter.
If you don't see a command prompt, try pressing enter.
$ python3 -m venv $HOME/www/python/venv
$ python3 -m venv $HOME/www/python/venv
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Successfully installed pip
Successfully installed pip
Cleaning up...
Cleaning up...
</syntaxhighlight>
}}


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.
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 ====
;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.
'''Note:''' It is Python best practice to use a file named <code>requirements.txt</code> to keep track of the library dependencies of applications.


<syntaxhighlight lang="shell-session">
{{Codesample|lang=shell-session|scheme=light|code=
$ cat > $HOME/www/python/src/requirements.txt << EOF
$ cat > $HOME/www/python/src/requirements.txt << EOF
flask
flask
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[...]
[...]
Successfully installed [...]
Successfully installed [...]
</syntaxhighlight>
}}


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


<syntaxhighlight lang="shell-session">
{{Codesample|lang=shell-session|scheme=light|code=
$ exit
$ exit
</syntaxhighlight>
}}
 
==== Create a 'hello world' WSGI application ====


Place the following code in <code>$HOME/www/python/src/app.py</code>:
;Create a 'hello world' WSGI application


<syntaxhighlight lang="python3">
{{Codesample|lang=shell-session|scheme=light|name=$HOME/www/python/src/app.py|code=
# -*- coding: utf-8 -*-
# -*- coding: utf-8 -*-
#
#
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def index():
def index():
   return 'Hello World!'
   return 'Hello World!'
</syntaxhighlight>
}}


'''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].  
'''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].  
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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.
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 ====
;Start the webservice
<syntaxhighlight lang="shell-session">
 
$ webservice --backend=kubernetes python start
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes python3.7 start
Starting webservice.
Starting webservice.
</syntaxhighlight>
}}
Once the webservice is started, navigate to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser, and see a 'Hello World!' message. It might take a few minutes until it is reachable.
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 ===
==== 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:
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>$HOME/www/python/src/app.py</code> in a variable named <code>app</code>.
* The application will have a WSGI entry point in <code>$HOME/www/python/src/app.py</code> in a variable named <code>app</code>.
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* Logs will be written to <code>$HOME/uwsgi.log</code>
* Logs will be written to <code>$HOME/uwsgi.log</code>


'''Expected file layout'''
;Expected file layout
<pre>
{{Codesample|lang=text|scheme=light|code=
$HOME
$HOME
  ├─ uwsgi.log
  ├─ uwsgi.log
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         │  └─ app.py
         │  └─ app.py
         └─ venv
         └─ venv
</pre>
}}


=== Troubleshooting ===
==== 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.  
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.  
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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:
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:


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


== Step 3: Add a configuration file ==
=== 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.
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.
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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.
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 ===
==== How to add a configuration file ====


==== Add PyYAML to the virtual environment ====
;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.  
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.  
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Python does not have built in support for parsing YAML files. Install a library to help out.
Python does not have built in support for parsing YAML files. Install a library to help out.


<syntaxhighlight lang="shell-session">
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes python shell
$ webservice --backend=kubernetes python3.7 shell
If you don't see a command prompt, try pressing enter.
If you don't see a command prompt, try pressing enter.
$ source $HOME/www/python/venv/bin/activate
$ source $HOME/www/python/venv/bin/activate
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Successfully installed pyyaml
Successfully installed pyyaml
$ exit
$ exit
</syntaxhighlight>
}}


==== Read configuration from a file ====
;Read configuration from a file


Update the <code>$HOME/www/python/src/app.py</code> file to read configuration from a <code>config.yaml</code> file in the same directory and get the greeting from the configuration file:
Update the <code>$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">
{{Codesample|lang=python3|scheme=light|name=$HOME/www/python/src/app.py|code=
# -*- coding: utf-8 -*-
# -*- coding: utf-8 -*-
#
#
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def index():
def index():
     return app.config['GREETING']
     return app.config['GREETING']
</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.
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">
{{Codesample|lang=shell-session|scheme=light|code=
$ 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
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GREETING: Goodnight moon!
GREETING: Goodnight moon!
EOF
EOF
</syntaxhighlight>Now restart the webservice:<syntaxhighlight lang="shell-session">
}}
Now restart the webservice:
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice restart
$ webservice restart
Restarting webservice...
Restarting webservice...
</syntaxhighlight>
}}


Once the webservice has restarted, navigate to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser and see the new 'Goodnight moon!' message.
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 ====
==== Troubleshooting ====
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If there is an error, look in <code>$HOME/uwsgi.log</code> and <code>$HOME/error.log</code> for an explanation.
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 ==
=== 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]].
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 ===
==== 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.
[https://pythonhosted.org/mwoauth/ mwoauth library] is used to handle most of the complexity of making OAuth requests to MediaWiki.


<syntaxhighlight lang="shell-session">
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice --backend=kubernetes python shell
$ webservice --backend=kubernetes python3.7 shell
If you don't see a command prompt, try pressing enter.
If you don't see a command prompt, try pressing enter.
$ source $HOME/www/python/venv/bin/activate
$ source $HOME/www/python/venv/bin/activate
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Successfully installed [...]
Successfully installed [...]
$ exit
$ exit
</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}}
<syntaxhighlight lang="python3">
{{Codesample|lang=python3|scheme=light|name=$HOME/www/python/src/app.py|code=
# -*- coding: utf-8 -*-
# -*- coding: utf-8 -*-
#
#
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     flask.session.clear()
     flask.session.clear()
     return flask.redirect(flask.url_for('index'))
     return flask.redirect(flask.url_for('index'))
</syntaxhighlight>
}}
{{Collapse bottom}}
{{Collapse bottom}}


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


==== Update the configuration to add OAuth secrets ====
;Update the configuration to add OAuth secrets


==== Add new configuration values to <code>$HOME/www/python/src/config.yaml</code> file to go with the new code ====
Add new configuration values to <code>$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].  
# [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://</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.
# 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)
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# Copy the ''consumer token'' and ''secret token'' values that are generated. These are needed for the config.yaml file.
# Copy the ''consumer token'' and ''secret token'' values that are generated. These are needed for the config.yaml file.


<syntaxhighlight lang="shell-session">
{{Codesample|lang=shell-session|scheme=light|code=
$ cat >> $HOME/www/python/src/config.yaml << EOF
$ cat >> $HOME/www/python/src/config.yaml << EOF
SECRET_KEY: $(python -c "import os; print repr(os.urandom(24))")
SECRET_KEY: $(python -c "import os; print repr(os.urandom(24))")
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CONSUMER_SECRET: the 'secret token' value from your OAuth consumer registration
CONSUMER_SECRET: the 'secret token' value from your OAuth consumer registration
EOF
EOF
</syntaxhighlight>
}}


==== Restart the webservice====
;Restart the webservice
<syntaxhighlight lang="shell-session">
{{Codesample|lang=shell-session|scheme=light|code=
$ webservice restart
$ webservice restart
Restarting webservice...
Restarting webservice...
</syntaxhighlight>Once the webservice has restarted, navigate to <code><nowiki>https://tools.wmflabs.org/</nowiki><TOOL NAME>/</code> in your web browser to see the new landing page.
}}
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.
Try using the ''login'' and ''logout'' links to test out the OAuth integration.
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=== bash: webservice: command not found ===
=== bash: webservice: command not found ===
# Check shell prompt.  
# Check shell prompt.  
# If it ends in <code>@interactive $</code>, you are inside a Kubernetes shell (<code>webservice --backend=kubernetes python shell</code>).  
# If it ends in <code>@interactive $</code>, you are inside a Kubernetes shell (<code>webservice --backend=kubernetes python3.7 shell</code>).  
#:* The <code>webservice</code> command is only available on the Toolforge bastions.  
#:* 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.
# 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 set for <code>CONSUMER_KEY</code> and <code>CONSUMER_SECRET</code>
# Double check the values 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>  
# Add <code>Debug: True</code> to <code>config.yaml</code>  
# Check <code>uwsgi.log</code> for more information.  
# Check <code>uwsgi.log</code> for more information.  
'''Note:''' This needs a <code>webservice restart</code> to take effect.
'''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 ==
== Next Steps ==
Now that your Flask OAuth tool is set-up here are some next steps to consider:
Now that your Flask OAuth tool is set-up here are some next steps to consider:


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* Use the [[User:Legoktm/toolforge library|toolforge library]] to set a nice user agent.
* 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.
* 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 ==
== See also ==
* [[Phab:source/tool-my-first-flask-oauth-tool/|Git repository 'tool-my-first-flask-oauth-tool' on Phabricator]]
* [[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]]
* [[toolforge:my-first-flask-oauth-tool/|My-first-flask-oauth-tool on Toolforge]]
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* [[Help:Toolforge/My first NodeJS OAuth tool]]
* [[Help:Toolforge/My first NodeJS OAuth tool]]


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

Latest revision as of 17:22, 30 August 2021

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 Toolforge as quickly as possible. The application is written using the Flask framework.

The guide will teach you how to:

Getting started

Prerequisites

Skills

  • Basic knowledge of Python
  • Basic knowledge of SSH
  • Basic knowledge of the Unix command line
  • Familiarity with OAuth terminology would be nice but not required

Accounts

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 OAuth authentication

Step 1: Create a new tool account

  1. Create a new tool account.
    • For the examples in this tutorial, <TOOL NAME> is used to indicate places where your unique tool name is used in another command.
  2. SSH to login.toolforge.org.
    • If your local username is different from your shell account name on Toolforge, you will need to include your Toolforge shell account name in your ssh command (i.e. <shell_username>@login.toolforge.org).
  3. Run become <TOOL NAME> to change to the tool user.

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 allows the 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. 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.

$ webservice --backend=kubernetes python3.7 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 python3 -m venv $HOME/www/python/venv 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 requirements.txt to keep track of the library dependencies of applications.

$ 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.

$ exit
Create a 'hello world' WSGI application
$HOME/www/python/src/app.py
# -*- 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 GPLv3+ license.

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 this Toolforge policy.

Start the webservice
$ webservice --backend=kubernetes python3.7 start
Starting webservice.

Once the webservice is started, navigate to https://<TOOL NAME>.toolforge.org/ 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 'convention over configuration' design with the following expectations:

  • The application will have a WSGI entry point in $HOME/www/python/src/app.py in a variable named app.
  • Python libraries will be loaded from a virtualenv located in $HOME/www/python/venv.
  • Logs will be written to $HOME/uwsgi.log
Expected file layout
$HOME
 ├─ uwsgi.log
 └─ www
     └─ python
         ├─ src
         │   └─ app.py
         └─ venv

Troubleshooting

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

One Unix utility to use for this 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

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 app.config 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.

$ webservice --backend=kubernetes python3.7 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:

$HOME/www/python/src/app.py
# -*- 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, navigate to https://<TOOL NAME>.toolforge.org/ in your web browser and see the new 'Goodnight moon!' message.

Troubleshooting

If there is an error, 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 the application. For 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 python3.7 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 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 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
$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://<TOOL NAME>.toolforge.org/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)
    • You will be able to use your own account before the consumer has been approved.
  5. Copy the consumer token and secret token values that are generated. These are needed for the 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, navigate to https://<TOOL NAME>.toolforge.org/ 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

  1. Check shell prompt.
  2. If it ends in @interactive $, you are inside a Kubernetes shell (webservice --backend=kubernetes python3.7 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 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.

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

  1. Run become <TOOL NAME> 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 flask.session['access_token'] to make API calls as the authorized user.
  • Explore the mwclient library to make interacting with the MediaWiki Action API easier.
  • Publish your source code in a git repository.
  • Add a co-maintainer.
  • Create a description page for your tool.
  • Use the 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 FLASK_APP=app.py FLASK_ENV=development flask run). 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.

Communication and support

We communicate and provide support through several primary channels. Please reach out with questions and to join the conversation.

Communicate with us
Connect Best for
Phabricator Workboard #Cloud-Services Task tracking and bug reporting
IRC Channel #wikimedia-cloud connect
Telegram bridge
mattermost bridge
General discussion and support
Mailing List cloud@ Information about ongoing initiatives, general discussion and support
Announcement emails cloud-announce@ Information about critical changes (all messages mirrored to cloud@)
News wiki page News Information about major near-term plans
Cloud Services Blog Clouds & Unicorns Learning more details about some of our work
Wikimedia Technical Blog techblog.wikimedia.org News and stories from the Wikimedia technical movement

See also