OmniAuth Slack, a Ruby Gem

⚠ NOTICE: You are viewing the README of the master branch of the ginjo fork of the omniauth-slack gem. This document may refer to features not yet released. Conversely (inversely?) this branch may contain features and changes not yet documented.

To view current or previous releases:

Version	Release Date	README
v2.5.0 (ginjo)	2020-06-17	https://github.com/ginjo/omniauth-slack/blob/v2.5.0/README.md
v2.4.1 (ginjo)	2018-09-18	https://github.com/ginjo/omniauth-slack/blob/v2.4.1/README.md
v2.4.0 (ginjo)	2018-08-28	https://github.com/ginjo/omniauth-slack/blob/v2.4.0/README.md
v2.3.0 (kmrshntr)	2016-01-06	https://github.com/kmrshntr/omniauth-slack/blob/master/README.md

OmniAuth Slack, a Ruby Gem

The omniauth-slack gem contains the Slack OAuth2 strategy for OmniAuth and supports the Slack OAuth2 v2 API and the Slack OAuth2 v1 API.

This Gem supports Slack v2 API bot and user tokens, as well as v1 API workspace apps and tokens. Slack "classic" apps and tokens should also work but are not fully tested.

Omniauth-slack does not enforce a Ruby version constraint. The Gem will work with Ruby versions 2.3 through 2.6.x. Older versions of Ruby may work but are not tested. Ruby version 2.7.x may work but is not yet tested.

Before You Begin

OmniAuth Slack is implemented through the OmniAuth gem, so you should familiarize yourself with the basics of OmniAuth.

OmniAuth Slack authorizes Slack users on behalf of a defined Slack application. If you don't already have an application defined on Slack, sign into the Slack application dashboard and create an application. Take note of your API keys.

While you're in the application settings, add a Redirect URL to your application (under the OAuth2 & Permissions section), something simple like http://localhost:3000/ or https://myslackapp.com/. The URL doesn't have to be accessible to the public internet, but it should be accessible to your development machine.

Using This Strategy

First start by adding this gem to your Gemfile:

  gem 'ginjo-omniauth-slack', require:'omniauth-slack'

Or specify the latest HEAD (development) version from the ginjo repository:

  gem 'ginjo-omniauth-slack', require:'omniauth-slack', git: 'https://github.com/ginjo/omniauth-slack'

Next, tell OmniAuth about this provider.

For a Rails app, your config/initializers/omniauth.rb file should look like this:

  Rails.application.config.middleware.use OmniAuth::Builder do
    provider :slack, 'API_KEY', 'API_SECRET', scope: 'string-of-scopes'
  end

Replace 'API_KEY' and 'API_SECRET' with the relevant values you obtained from the Slack application setup. Replace 'string-of-scopes' with a space-separated string of Slack API scopes.

For a Sinatra app:

  require 'sinatra'
  require 'omniauth-slack'

  use OmniAuth::Builder do |env|
    provider :slack,
      ENV['SLACK_OAUTH_KEY_WS'],
      ENV['SLACK_OAUTH_SECRET_WS'],
      scope: 'string-of-scopes'
  end

If you are using Devise then it should look like this:

  Devise.setup do |config|
    # other stuff...

    config.omniauth :slack, ENV['SLACK_APP_ID'], ENV['SLACK_APP_SECRET'], scope: 'string-of-scopes'

    # other stuff...
  end

To manually install and require the gem:

  # shell
  gem install ginjo-omniauth-slack

  # ruby
  require 'omniauth-slack'

Scopes

Slack lets you choose from a number of scopes supporting one or more of the classic, workspace, and v2 apps and token types.

Important: You cannot request both identity scopes and non-identity scopes in a single authorization request, within the same scope field (scope or user_scope).

If you need to combine Add to Slack scopes with those used for Sign in with Slack, you may want to configure two providers:

  provider :slack, 'API_KEY', 'API_SECRET', name: :sign_in_with_slack, scope: 'identity.basic'
  provider :slack, 'API_KEY', 'API_SECRET', scope: 'team:read,users:read,identify,bot'

Use the first provider to sign users in and the second to add the application, and deeper capabilities, to their team.

The Sign-in-with-Slack approval flow handles quick authorization of users with minimally scoped requests. Deeper scope authorizations are acquired with further passes through the authorization cycle.

This works because Slack scopes are additive: Once you successfully authorize a scope, the token will possess that scope forever, regardless of what flow or scopes are requested at future authorizations (removal of scope requires revocation of the token or uninstallation of the Slack app from the team).

v2 API scope fields

The Slack v2 API allows two different scope fields in the authorization request.

Scopes passed in the scope field are requesting a bot token.
Scopes passed in the user_scope field are requesting a user token.

There must be at least one scope listed in either of the fields for most (but not all) v2 API requests.

The rule mentioned above, "... don't mix identity scopes with other scopes..," applies to v2 API requests as well, however only for the user_scope field. The scope field in the v2 API does not accept identity scopes.

Options

Options for omniauth-slack are specified in the provider block, as shown above, and all are optional except for scope and/or user_scope.

Some of these options can also be given at runtime in the authorization request url (see pass_through_params below).

More information on provider and authentication options can be found in omniauth-slack's supporting gems omniauth, oauth2, and omniauth-oauth2.

:scope and/or :user_scope => space-delimited-string-of-scopes

required

  :scope => 'string-of-space-separated-scopes'

  # and/or (v2 API only)
  :user_scope => '...'

Specify the scopes for the authorization request.

team: string

optional

team_domain: string

optional

  :team => 'team-id',
  
  # and/or
  
  :team_domain => 'my_team_domain'

Requests authentication against a specific team.

If you don't pass a team param, the user will be allowed to choose which team they are authenticating against. Passing this param ensures the user will auth against an account on that particular team.

If you need to ensure that the users are authenticating against a specific team_id, you can pass the :team option in your provider block:

  provider :slack, 'API_KEY', 'API_SECRET', scope: 'identify,read,post', team: 'XXXXXXXX'

If the user is not already signed in to the Slack team specified, they will be given an option to select a team first.

Another (possibly undocumented) way to specify team is by passing in the :team_domain parameter. In contrast to setting :team, setting :team_domain will force authentication against the specified team (credentials permitting of course), even if the user is not signed in to that team. However, if the user is already signed in to that team, specifying the :team_domain alone will not let the user skip the Slack authorization dialog, as is possible when you specify :team.

Sign in behavior with team settings and signed in state can be confusing. Here is a breakdown based on Slack documentation and observations while using omniauth-slack.

Team settings and sign in state vs Slack OAuth2 behavior.

Setting and state	Will authenticate against specific team	Will skip authorization approval - The elusive unobtrusive Sign in with Slack
using `:team`, already signed in	🔹	🔹
using `:team`, not signed in		🔹
using `:team_domain`, already signed in	🔹
using `:team_domain`, not signed in	🔹
using `:team` and `:team_domain`, already signed in	🔹	🔹
using `:team` and `:team_domain`, not signed in		🔹
using no team parameters

Slack's authorization process will only skip the authorization approval step, if in addition to the above settings and state, ALL of the following conditions are met:

Token has at least one identity scope previously approved.
Current authorization is requesting at least one identity scope.
Current authorization is not requesting any scopes that the token does not already have.
Current authorization is not requesting any non-identity scopes (but it's ok if the token already has non-identity scopes).

redirect_uri: string

String optional

  :redirect_uri => 'https://<defaults-to-the-app-origin-host-and-port>/auth/slack/callback'

This setting overrides the :callback_path setting.

Set a custom redirect URI in your app, where Slack will redirect-to with an authorization code. The redirect URI, whether default or custom, MUST match a registered redirect URI in your app settings on api.slack.com.

callback_path: string

optional

  :callback_path => '/auth/slack/callback'

This setting is ignored if :redirect_uri is set.

Set a custom callback path (path only, not the full URI) for Slack to redirect-to with an authorization code. This will be appended to the default redirect URI only. If you wish to specify a custom redirect URI with a custom callback path, just include both in the :redirect_uri setting.

skip_info: boolean

optional

  :skip_info => false

Skip building the InfoHash section of the AuthHash object.

If set, only a single api request will be made for each authorization. The response of that authorization request may or may not contain user and email data.

pass_through_params: array-of-strings

optional

Options for scope, team, team_domain, and redirect_uri can also be given at runtime via the query string of the omniauth-slack authorization endpoint URL /auth/slack?team=.... The scope, team, and redirect_uri query parameters will be passed directly through to Slack in the OAuth2 GET request:

 https://slack.com/oauth/authorize?scope=identity.basic,identity.email&team=team-id&redirect_uri=https://different.subdomain/different/callback/path

The team_domain query parameter will be inserted into the authorization GET request as a subdomain https://team-domain.slack.com/oauth/authorize.

NOTE: Allowing redirect_uri, scope, or team_domian to be passed to Slack from your application's public interface (https://myapp.com/auth/slack?scope=...) is a potential security risk. As of omniauth-slack version 2.5.0, the default is to NOT allow scope, redirect_uri, or team_domain pass-through options at runtime, unless they are listed in the :pass_through_params option. The team param is allowed to pass through as a default.

To block all pass-through options.

  provider :slack, KEY, SECRET, pass_through_params:nil

To allow all pass-through options.

  provider :slack, KEY, SECRET, pass_through_params: %w(team scope redirect_uri team_domain)

client_options: hash-of-client-options

optional

Client options control the behavior of the OAuth2::Client, which handles the http requests and redirects during the OmniAuth OAuth2 cycle. Here is the current default client_options.

  option :client_options, {
    site: 'https://slack.com',
    authorize_url: '/oauth/v2/authorize',
    token_url: '/api/oauth.v2.access',
    auth_scheme: :basic_auth,
    raise_errors: false, # MUST be false to allow Slack's get-token response from v2 API.
    history: Array.new,
  }

Generally, you can leave this option alone, but there is one case where you need it: If you want to use Slack's v1 (legacy, classic, whatever) API, you need to change the authorization and token endpoints.

To switch to Slack v1 API, change to these options within client_options:

authorize_url: '/oauth/authorize',
token_url: '/api/oauth.access',

Slack v2 API

Slack is recommending the v2 API for all new Slack apps. This gem supports Slack's v2 API and its associated tokens and apps. The v2 API endpoints are now the default in omniauth-slack.

The omniauth-slack gem does not put a version constraint on the OAuth2 gem, so as to remain compatible with installations using earlier versions of OAuth2 (and not needing Slack's v2 API). However, use of omniauth-slack with Slack's new API requires a minimum version of the OAuth2 gem.

Using omniauth-slack with Slack's v2 API requires OAuth2 gem version 1.4.4+

Make sure your application is loading the OAuth2 gem version 1.4.4+. In most cases, Bundler and the gem dependency tree will sort this out for you. But some gems or gem combinations may install an older OAuth2 gem. If so, try something like this in your Gemfile:

  gem 'oauth2', '~> 1.4.4'
  
  # or
  
  gem 'oauth2', '>= 1.4.4'

The reason behind this

Tokens returned from the v2 API may not always conform to the OAuth2 spec, and therefore may raise errors in the OAuth2 gem during the callback phase, even if the token response from Slack's v2 API is successful from Slack's point of view.

To avoid this issue, the omniauth-slack strategy client_options must be set with {raise_errors: false}, which will only have the desired effect on the OAuth2 gem version 1.4.4 and above. This raise_errors option is now the default in the omniauth-slack gem.

Access Tokens

While the core OAuth2 access-token is a simple string, the OAuth2 gem packages it along with other data returned from the /api/oauth.access call, as an AccessToken instance. The AccessToken contains everything you need to make Slack API requests: the actual token string, the expiration data (if any), the team, user, scope, and an OAuth2::Client instance with the API key and secret.

The AccessToken generated by omniauth-slack also has additional features, such as has_scope?(list-of-scopes), which queries the token's awarded scopes. This is handy for Slack Workspace apps and their multi-dimensional scopes, but it works for any Slack token type.

Storage

Use the AccessToken#to_hash method to prepare the token for serialization and storage in a database. This method strips off all unnecessary objects and leaves just the data.

Retrieval

When you want to reconstitute the access-token from a stored hash or string, use the OmniAuth::Slack::OAuth2::AccessToken.from_hash method. Or use omniauth-slack's convenience method:

access_token = OmniAuth::Slack.build_access_token(key, secret, access_token_string_or_hash)

Usage

Once you have a valid AccessToken instance, you can do things like:

  access_token.get('/api/apps.permissions.users.list')

  access_token.refresh

  access_token.post('/api/chat.postMessage', params: {channel: channel_id, text: message})

To extract data from the API response, call parsed on the response object.

  access_token.get('/api/channels.list').parsed['channels']

  # => [{'id' => 1, 'name' => ...}, {'id' => ...}]

The Auth Hash

Each Successful OmniAuth authorization places an AuthHash object in the environment env['omniauth.auth']. The AuthHash is just an enhanced hash object containing data from theOAuth2 response received from the get-token API call made during the OmniAuth callback phase. See OmniAuth's documentation for the AuthHash schema definition.

With the growing number of multi-dimensional data structures for the various token response objects, mapping of response data to the AuthHash object has become increasingly complex. To establish a meaningful mapping that serves the downstream application's needs, the functionality and goals of the application need to be considered.

The omniauth-slack gem will now copy the access-token hash to the AuthHash info section, but it will no longer be mapping specific data points from the access-token to specific fields in the AuthHash info section (other than info fields that are 'required' by the OmniAuth::AuthHash schema spec).

Application developers are welcome to define their own info section directly within the omniauth-slack strategy. And the same customization can be done for any of the top-level AuthHash sections.

  class OmniAuth::Strategies::Slack
    info do
      # Should return a hash object.
      # Will be called during the callback-phase.
      # Will be evaluated in the context of the strategy instance.
      # Strategy options are available in this context.
      # Current access_token (assuming it was successful) is available in this context.
    end
  end

If you want to build your own info section and have it appended to omniauth-slack's default info section, then subclass the strategy and use that subclass as your OmniAuth provider.

  class MyCustomStrategy < OmniAuth::Strategies::Slack
    info do
      # Should return a hash object.
      # Will be called during the callback-phase.
      # Will be evaluated in the context of the strategy instance.
      # Strategy options are available in this context.
      # Current access_token (assuming it was successful) is available in this context.
    end
  end
  
  # ...
  
  use OmniAuth::Builder do
    provider MyCustomStrategy, SLACK_OAUTH_KEY, SLACK_OAUTH_SECRET, scope: ...
  end

The credentials section of the AuthHash will contain the access-token string, the awarded scopes, and any other essential authentication information returned in the OAuth2 response.

The extra section contains two hash keys:

:scopes_requested hash, which are the scopes requested during the current authorization.
:raw_info hash, which contains the raw response object from any API calls made during the callback phase.

The OAuth2 Cycle

The OAuth2 cycle is a three-way dance between the user's browser, the OAuth2 provider (Slack API), and the application server (your Slack App). It should work this way for any OAuth2 provider, including Slack.

The user/browser makes a request to https://slack.com/oauth/authorize, passing the application's client-id, requested-scopes, and optionally state, team-id, and redirect-uri. Slack then runs the user through the authorization dialogs.
Upon successful authorization, Slack redirects the browser to the application's callback url (or redirect_uri in Slack's terms) with a short-lived authorization code, for example:

https://yourapp.com/auth/slack/callback?code=ABCDE87364
Omniauth-slack intercepts this request and exchanges the code, via Slack API, for a valid access-token.

And that's it. Control is then given to your application's /auth/slack/callback action.

The next step would be the application storing the access-token, maybe making additional API requests, and then rendering a page to the browser or redirecting to another action. In a working app, a session would store a reference to the token, and the token would be stored in a database. Then for every request from that user, a valid access-token would be accessible and usable to make further API requests.

The OAuth2 Cycle with OmniAuth Slack

While the browser experience may appear simple, there's quite a lot happening behind the scenes in the omniauth-oauth2 library that omniauth-slack is derived from. Omiauth-slack is Rack middleware loaded in the stack behind your main app, and it handles the above sequence(s) before your application receives the request(s).

So lets run through the cycle again and take a closer look.

1. The user/browser makes a request to your application at http://yourapp.com/auth/slack. This URI could be the href of your signin-with-slack or add-to-slack button.
  
  Your application's server-side code doesn't need to know about this endpoint, and it doesn't need to define an action for it. Omniauth-slack middleware recognizes this URI as the authorization request.
2. Omniauth-slack intercepts this request, considers local configuration, stores some data in a session variable, and then redirects the browser, with the necessary data embedded in the URI params, to Slack's authorization URI.
  
  OmniAuth calls this the request phase, and your application sees none of it.
1. Having been redirected by omniauth-slack, the browser makes an authorization request to https://slack.com/oauth/authorize, passing the application's client-id, requested-scopes, and optionally state, team-id, and redirect-uri. This request contains everything Slack needs to authenticate the user and authorize access to Slack's API functions and data.
2. Slack leads the user through any dialogs necessary to complete the authorization.
  
  Depending on the setup, the requested (and awarded) scopes and permissions, and Slack's internal logic, this cycle could appear as a series of dialogs or as a simple request/response. If identity scopes were requested (signin-with-slack flow), and a team-id was passed in the params, and the given scopes were previously authorized, Slack may grant authorization without requiring the user to click on any dialogs at all.
  
  Meanwhile, the application server and omniauth-slack are patiently waiting and have no idea what Slack, or the user, are doing at this point.
Upon successful authorization, Slack redirects the browser to the application's callback url (or redirect_uri) with a short-lived authorization code, for example:

https://yourapp.com/auth/slack/callback?code=ABCDE87364.

Your application needs to define an endpoint for /auth/slack/callback, but omniauth-slack does all of its work before your app even sees the request.
1. Omniauth-slack intercepts this request, and exchanges the authorization code for a valid access-token by making an API request to https://slack.com/api/oauth.access.
  
  The oauth.access response contains an access-token (and possibly other data) which omniauth-slack stores in the Rack env for later use by your application.
  
  OmniAuth refers to this part of the process as the callback phase, and you don't see any of it (Rack middleware magic).
2. Rack then passes this callback request to your app, and you are at the logical beginning of whatever action you defined for /auth/slack/callback.
  
  There is a lot of data available in the request env['omniauth.auth'] and env['omniauth.strategy']. There are also other env variables defined by omniauth and omniauth-slack. See the gem docs for more about those.
  
  At this point, you will likely want to grab the env['omniauth.auth'] hash and the env['omniauth.strategy'].access_token object. Use the access-token to make further API requests, or store the token and auth_hash for later retrieval.
  
  See the note about access-tokens below.

Slack Workspace Apps

This gem provides support for Slack's Workspace apps (now legacy). There are some important differences between Slack's classic apps and the new Workspace apps. The main points to be aware of when using omniauth-slack with Workspace Apps are:

Workspace app tokens are issued as a single token per team. There are no user or bot tokens. All Workspace app API calls are made with the Workspace token. Calls that act on behalf of a user or bot are made with the same token.
The available api calls and the scopes required to access them are different in Workspace apps.
The AuthHash.credentials.scopes value, returned from a successful authentication, is a hash with each value containing an array of scopes. The usual scope key will not have a value.

OmniAuth Slack Basic Examples

Don't forget to set up your Slack app on api.slack.com.

Sinatra Example

Create a Sinatra project directory, then add these files.

simple_app.rb

  require 'omniauth-slack'
  require 'sinatra'
  require 'yaml'

  enable :sessions

  # optional
  #set :port, '9292'
  #set :bind, '0.0.0.0'

  use OmniAuth::Builder do
    provider :slack, SLACK_OAUTH_KEY, SLACK_OAUTH_SECRET, scope:'identity:read:user'
  end

  get '/auth/slack/callback' do
    content_type 'text/yaml'
    { auth_hash:    env['omniauth.auth'],
      access_token: env['omniauth.strategy'].access_token
    }.to_yaml
  end

Gemfile

  source 'https://rubygems.org'
  gem 'ginjo-omniauth-slack'   #, git:'https://github.com/ginjo/omniauth-slack'
  gem 'sinatra'
  gem 'puma'

Put those in their respective files, fill in your Slack OAuth2 credentials, then launch.

bundle install
bundle exec ruby super_simple.rb

Then point your browser to

http://<host-and-port-recognized-in-slack-redirect-uri-list>/auth/slack

When a successful authorization cycle completes, your browser should end up with a yaml representation of the auth_hash and access_token objects. What happens next is entirely up to your application.

Rails Example

Create a rails project, then add or modify these files. Note that this is not necessarily the best way to do this in a production system. It's just a demonstration of the bare necessities to get omniauth-slack working in Rails.

config/initializers/middleware.rb

  require 'omniauth-slack'

  Rails.application.config.middleware.use OmniAuth::Builder do
    provider :slack, SLACK_OAUTH_KEY, SLACK_OAUTH_SECRET, scope:'identity:read:user'
  end

app/controllers/auth_controller.rb

  class AuthController < ApplicationController
    def callback
      render plain: { access_token: request.env['omniauth.strategy'].access_token.to_hash,
        auth_hash:  request.env['omniauth.auth']
      }.to_yaml
    end
  end

config/routes.rb

  get 'auth/slack/callback', to: 'auth#callback'

Gemfile

  gem 'ginjo-omniauth-slack'   #, git:'https://github.com/ginjo/omniauth-slack'

Don't forget to fill in your Slack API credentials. Then start up Rails, and point your browser to

http://<host-and-port-recognized-in-slack-redirect-uri-list>/auth/slack

When a successful authorization cycle completes, your browser should end up with a yaml representation of the auth_hash and access_token objects. What happens next is entirely up to your application.

Advanced / Experimental

Deep debug with ENV['OMNIAUTH_SLACK_DEBUG']=true. Will output a LOT of detailed TRACE log items. Only use this for debugging during development.

An optional OmniAuth::Slack::VerifySlackSignature middleware class handles signature verification for incoming Slack requests. This is helpful if you receive Slack events in your application.

  # In your rack middleware setup file.

  use OmniAuth::Slack::VerifySlackSignature do |config|
    config.app_id          = ENV['SLACK_APP_ID']
    config.signing_secret  = ENV['SLACK_SIGNING_SECRET']
  end
  
  # When legitimate incoming Slack request is received by your app:
  env['omniauth.slack.verification'] == true

  # When illegitimate incoming Slack request is received by your app:
  env['omniauth.slack.verification'] == false
  
  # When any other request is received by your app:
  env['omniauth.slack.verification'] == nil

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Add some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request

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.rubocop_todo.yml		.rubocop_todo.yml
.yardopts		.yardopts
CHANGELOG.md		CHANGELOG.md
Gemfile		Gemfile
LICENSE.txt		LICENSE.txt
README.md		README.md
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omniauth-slack.gemspec		omniauth-slack.gemspec

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OmniAuth Slack, a Ruby Gem

Before You Begin

Using This Strategy

Scopes

v2 API scope fields

Options

:scope and/or :user_scope => space-delimited-string-of-scopes

team: string

team_domain: string

Team settings and sign in state vs Slack OAuth2 behavior.

redirect_uri: string

callback_path: string

skip_info: boolean

pass_through_params: array-of-strings

client_options: hash-of-client-options

Slack v2 API

Using omniauth-slack with Slack's v2 API requires OAuth2 gem version 1.4.4+

The reason behind this

Access Tokens

Storage

Retrieval

Usage

The Auth Hash

The OAuth2 Cycle

The OAuth2 Cycle with OmniAuth Slack

Slack Workspace Apps

OmniAuth Slack Basic Examples

Sinatra Example

simple_app.rb

Gemfile

Rails Example

config/initializers/middleware.rb

app/controllers/auth_controller.rb

config/routes.rb

Gemfile

Advanced / Experimental

Contributing

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