Last updated 13 July 2020

Your cloud service probably has a web UI admin panel that your users log into to manage their resources. For example, a Memcache cloud service may offer a dashboard for web-based usage analytics and the ability to flush a cache.

Heroku customers can access your dashboard as well if you implement single sign-on as described in this document.

Summary

Heroku will generate a single sign-on token by combining the salt (a shared secret), timestamp, and resource ID. The user’s browser will be redirected to your site with this token. Your site can confirm the authenticity of the token, then create a user session and route them to the admin panel for their resource.

Testing SSO

We suggest creating a <your slug>-staging version of your add-on to test SSO and other add-on integration features. This <your slug>-staging add-on should point to staging versions of your integration infrastructure.

Salt, timestamp, and tokens

When you create an add-on (and consequently its manifest), the manifest fields include a randomly-generated sso_salt.

There are two tokens in an SSO request and either one may be used to log in the user, depending on what version of the Add-on Partner API you’re using. The v3 token is named resource_token. The legacy v1 token is named token.

Creating the Resource Token under v3

Under v3 of the Add-on Partner API, the resource_token is created using the following formula:

resource_token = sha1(resource_uuid + ':' + salt + ':' + timestamp)

• resource_uuid is the uuid that we provide for the resource in a provisioning request.
• salt comes from your add-on manifest.
• timestamp will be included in the parameters for the POST request.

For example, given these inputs:

resource_uuid = 11111111-1111-1111-1111-111111111111
salt = 2f97bfa52ca102f8874716e2eb1d3b4920ad0be4
timestamp = 1267597772

…the SSO resource_token will be:

SHA1("11111111-1111-1111-1111-111111111111:2f97bfa52ca102f8874716e2eb1d3b4920ad0be4:1267597772") =
4e9ce13ca328c6f3e2857b7de1724fd6c7c1c423

Creating the Resource Token under v1

Under v1 of the Add-on Partner API, the token is created using the following formula:

token = sha1(provider_id + ':' + salt + ':' + timestamp)

• provider_id is the value you created and returned from your cloud service during a response to provisioning request.
• salt comes from your add-on manifest.
• timestamp will be included in the parameters for the POST request.

For example, given these inputs:

provider_id = 123
salt = 2f97bfa52ca102f8874716e2eb1d3b4920ad0be4
timestamp = 1267597772

…the SSO token will be:

SHA1("123:2f97bfa52ca102f8874716e2eb1d3b4920ad0be4:1267597772") =
bb466eb1d6bc345d11072c3cd25c311f21be130d

Signing in the user on redirect

When the user clicks your add-on in their add-on menu, they will be directed via HTTP POST to a URL defined in your manifest.

Requests will look like:

POST <production/sso_url>
resource_id=<resource_id>&resource_token=<resource_token>&id=<id>&token=<token>&timestamp=<timestamp>&nav-data=<nav data>&email=<user's email address>

As shown, the data is form-encoded in the POST body.

• sso_url comes from your add-on manifest.
• resource_id is the uuid that we provide for the resource in the provisioning call.
• timestamp is a unix epoch timestamp.
• resource_token is computed using the formula above. When using the resource_id and resource_token, the id and token values should be ignored.

Legacy fields that can safely be ignored are:

• id and token – used only for the v1 salted token. Ignore if you are on v3 of the Add-on Partner API.
• nav-data contains information like the current app name and installed add-ons so the Heroku layout can build the appropriate view for the current app.

If the SHA1 hash you compute does not match the one passed in resource_token (or token if you’re using v1), the user should be shown a page with an HTTP status code of 403. If the timestamp is older than five minutes, they should also see a 403.

If the timestamp is current and the SHA1 hash matches, the user is authorized to access the resource in question.

You should create a user session through whatever method you normally use, possibly setting a cookie. The session should also store that it is a Heroku single sign-on, since what is displayed will be slightly different for Heroku customers than users logging in through your regular standalone service. Because user access can change at any time this SSO data should only be trusted for the duration of a session. We also suggest limiting session lifespan to 90 minutes.

Display user information in your site’s layout

There are additional form-encoded parameters sent in the SSO request to help your site display a context for the user. These include:

• user - the email address of the current user
• app - the Heroku app name that is in scope and the user came from.

These can be used to populate a template for the user info (and potentially fetch their Gravatar) as well as link back to the Dashboard for the app in context. For that, assuming the param came in as &app=your-app-name, link to https://dashboard.heroku.com/apps/your-app-name.

Sample code

Here’s a sample implementation of a v3 single sign-on endpoint written in Ruby/Sinatra:

post "/heroku/sso" do
  pre_token = params[:resource_id] + ':' + HEROKU_SSO_SALT + ':' + params[:timestamp]
  token = Digest::SHA1.hexdigest(pre_token).to_s
  halt 403 if token != params[:resource_token]
  halt 403 if params[:timestamp].to_i < (Time.now - 2*60).to_i

  account = Account.find(params[:resource_id])
  halt 404 unless account

  session[:user] = account.id
  session[:heroku_sso] = true
  redirect "/dashboard"
end

Removing non-relevant page elements

Once you have your site accepting single sign-on requests, the final step is to hide (or disable) page elements that are not relevant for Heroku customer SSO sessions. Some examples include:

• Change password
• Change account name
• Update billing information
• Log out

Heroku customers will manage all of these items through the Heroku Dashboard and CLI, and your add-on cannot update them in Heroku’s infrastructure.