Intermediate

Sign in with Slack

It's new and improved: Sign in with Slack helps users log into your service using their Slack profile.

If you already have an existing Sign in with Slack app that uses identity.* scopes, you can find legacy Sign in with Slack documentation here.

Otherwise, read on!


Overview

The Sign in with Slack flow allows users to grant their Slack profile information to your service.

It's based on the OpenID Connect standard, built on top of OAuth 2.0. The modern Sign in with Slack works with any package that successfully implements the standard.


Implementation packages

OpenID maintains a list of certified implementations of the OpenID Connect standard. We recommend you make use of one of these packages to take care of the boilerplate surrounding OAuth.

The path to Sign in With Slack is much easier with a package implementation at your disposal.

You'll create a Slack app, then configure your service so that you redirect users to the right Slack URL. Slack will send users back to your service along with the information you need.


Get started

Implementation of the Sign in with Slack follows the flow of our OAuth V2 process. If you're not familiar with that, you'll want to review the steps of negotiating that OAuth flow.

Here's an overview of the Sign in with Slack process. The key differences between Sign in with Slack and a typical OAuth flow for a Slack app are:

  • You redirect users to a special OpenID endpoint, /openid/connect/authorize, rather than /oauth/v2/authorize
  • You request the OpenID scopes—openid, email, and profile. If you've built a legacy Sign in with Slack app and want to know how the new flow relates to the legacy one, these scopes take the place of legacy identity.* scopes.
  • You exchange your access code for an access token using an OpenID method, /openid.connect.token, rather than oauth.v2.access.
  • You receive the standard OpenID response sent to your redirect URI, with the expected fields encoded in the id_token.
  • You use the openid.connect.userInfo method to retrieve updated user information. Again, if you're familiar with legacy Sign in with Slack, you'll use this method instead of users.identity.

Next up, we'll go through the flow in more detail.

App setup

First, make a Slack app:

Create a new Slack app

Fill out your App Name and select the Development Workspace where you'll play around and build your app. Don't fuss too much over either field—no matter what workspace you select, you'll still be able to distribute your app to other workspaces if you choose.

Navigate to the OAuth & Permissions section and configure a Redirect URL to match your service. The Redirect URL signifies where Slack should redirect users when they complete the OAuth flow. If you're using ngrok, use the ngrok public forwarding host as the root.

Discover information on Slack OpenID endpoints

Slack provides a discovery endpoint so that your OpenID Connect Relying Party can discover which endpoints to call. Our Well Known endpoint is accessible at:

https://slack.com/.well-known/openid-configuration

The response follows the OpenID standard, which looks like:

{
    "issuer": "https://slack.com",
    "authorization_endpoint": "https://slack.com/openid/connect/authorize",
    "token_endpoint": "https://slack.com/api/openid.connect.token",
    "userinfo_endpoint": "https://slack.com/api/openid.connect.userInfo",
    "jwks_uri": "https://slack.com/openid/connect/keys",
    "scopes_supported": ["openid","profile","email"],
    "response_types_supported": ["code"],
    "response_modes_supported": ["form_post"],
    "grant_types_supported": ["authorization_code"],
    "subject_types_supported": ["public"],
    "id_token_signing_alg_values_supported": ["RS256"],
    "claims_supported": ["sub","auth_time","iss"],
    "claims_parameter_supported": false,
    "request_parameter_supported": false,
    "request_uri_parameter_supported": true,
    "token_endpoint_auth_methods_supported": ["client_secret_post","client_secret_basic"]
}

Request with scopes

Send users into the Sign in with Slack authorization flow with a button or other redirect. If you're at all unsure of what that should look like, check out our design guidelines for tips on how to make the experience pleasant for your users.

You should redirect users to the following URL:

https://slack.com/openid/connect/authorize

Your request should have the standard OpenID Connect form, which is why it pays to use a pre-implemented package.

Here's an example:

  GET /openid/connect/authorize?
    response_type=code
    &scope=openid%20profile%20email
    &client_id=s6BhdRkqt3
    &state=af0ifjsldkj
    &team=T1234
    &nonce=abcd
    &redirect_uri=https%3A%2F%2Fclient.example.org%2Fcb HTTP/1.1
  Host: https://slack.com

Here's a quick explanation of the parameters:

  • The response_type=code parameter indicates that you're asking for a temporary access code to then exchange for an access token.
  • The scope field indicates which permissions you want the user to grant you (in this case, the base openid information plus profile and email).
  • The client_id field signifies your app's ID. You can find it in your app config under Basic Information.
  • The state parameter should be used to avoid forgery attacks—pass in a value that's unique to the user you're authenticating and check it when you receive a temporary authorization code.
  • The nonce parameter is used to verify that the entire flow has completed with no forgery. You can verify the nonce in the response you receive from the final token exchange to make sure it's the same as what you pass here.
  • The redirect_uri is where Slack will send the user back to, along with the temporary authorization code, once the user okays your app. You can specify a more specific redirect_uri than the one in your app config here— but it must be either an exact match or a subdirectory of one of the redirect URLs in your app config.

Your app will always request openid—the base scope you always need to request in any Sign in with Slack flow—and may request email and profile as well.

Exchange

After the user successfully grants your app permission to access their Slack profile, they'll be redirected back to your service along with the typical code that signifies a temporary access code. Exchange that code for a real access token using the /openid.connect.token method.

You can check that method's documentation for a full list of parameters to pass. As an overview: you'll pass the code as well as your app's client_secret, client_id, and a redirect_uri.

Response

After calling the /openid.connect.token method, you'll receive a standard OpenID response:

{
  "ok": true,
  "access_token": "xoxp-25259531569-25259531633-1115294117523-7f41783ecc1056a1d96902642c7f27d3",
  "token_type": "Bearer",
  "id_token": "eyJhbGc..."
}

id_token is a standard JSON Web Token (JWT). You can decode it with off-the-shelf libraries in any programming language, and most packages that handle OpenID will handle JWT decoding.

If you've requested openid email profile scopes, the token response decodes into an object like:

{
  "iss": "https://slack.com",
  "sub": "U0R7MFMJM",
  "aud": "25259531569.1115258246291",
  "exp": 1626874955,
  "iat": 1626874655,
  "auth_time": 1626874655,
  "nonce": "abcd",
  "at_hash": "tUbyWGBHe0V32FJEupkgVQ",
  "https://slack.com/team_id": "T0RR",
  "https://slack.com/user_id": "U0JM",
  "email": "bront@slack-corp.com",
  "email_verified": true,
  "date_email_verified": 1622128723,
  "locale": "en-US",
  "name": "brent",
  "given_name": "",
  "family_name": "",
  "https://slack.com/team_image_230": "https://secure.gravatar.com/avatar/bc.png",
  "https://slack.com/team_image_default": true
}

Some additional fields might be included in the payload.

Make sure to verify that the nonce returned in the JWT payload is the same as the nonce you supplied to authorize.

That's it! Your Sign in with Slack flow has officially completed. Now you can obtain updated user info whenever you want for that authenticated user.

Get updated user info

Once you've obtained a user access token from the Sign in with Slack flow, you can use the openid.connect.userInfo method to get updated user information, like their profile image and team image. Read up on the documentation there for more details on the exact response to expect.

Token rotation

Token rotation is supported with Sign in with Slack. It works exactly like regular token rotation, except with the Sign in Slack token exchange endpoint. You'll pass a grant_type=refresh_token and use a refresh_token parameter to obtain a new access token from openid.connect.token.


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Migrate a legacy Sign in with Slack app

If you already have a legacy Sign in with Slack app, it's easy to migrate to the current flow. Request the new OpenID scopes, reconfigure your authorization URL, parse the new response from openid.connect.token, and you're good to go.

Here's a map of what legacy Sign in with Slack feature corresponds to what modern feature:

Enjoy your modern Sign in with Slack app! If you want to get even more nitty gritty details on how best to present a pleasant experience to users, read on for some design guidelines.


Design guidelines

Here are some basic guidelines for the Sign in with Slack button:

  • Show the button prominently
  • The Slack logo should always be present.
  • The text should always say Sign in with Slack, with ‘S’ capitalized.
  • Use the same size as other sign in options
  • Make it visible and keep it above the fold.

Here's some specific size guidelines: A max size button should be:

  • 296px (width) x 56px (height)
  • 18px font Lato bold
  • Logo : 24px x 24px

A minimum size button shoulld be:

  • 224px (width) x 44px (height)
  • 14px font Lato bold
  • Logo : 16px x 16px

A default size button should be:

  • 256px (width) x 48px (height)
  • 16px font Lato bold
  • Logo : 20px x 20px

For a center-aligned logo, use:

  • Margin-between : 12px

For a border-aligned logo, use:

  • Margin-left : 16px

For a default theme, use:

  • Background color : #FFFFFF
  • Font color : #000000
  • Border color : #DDDDDD

For a dark theme, recommended only for spaces with sufficient contrast, use:

  • Background color : #4A154B
  • Font color : #FFFFFF
  • Border : none

Assets

Please use these assets when presenting Sign in with Slack.

This HTML snippet references our CDN-hosted buttons:

<img src="https://platform.slack-edge.com/img/sign_in_with_slack.png" srcset="https://platform.slack-edge.com/img/sign_in_with_slack.png 1x, https://platform.slack-edge.com/img/sign_in_with_slack@2x.png 2x" />

If you want to host the assets yourself, please download these images:

Download PNG (170px by 40px)

Download PNG (Retina, 344px by 80px)

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