Devise OmniAuth with a Multi-tenant Rails 5 App - ruby-on-rails

Question

Here is the situation. I have a multi-tenant rails app using the apartment gem where I need to implement a LinkedIn OmniAuth Strategy.
As you can see by my routes, Devise users, and the associated routes, are only persisted on the individual schemas of the subdomains.
Example Route:
Good: https://frank.example.io/users/sign_in
Bad: https://example.io/users/sign_in
Routes
class SubdomainPresent
def self.matches?(request)
request.subdomain.present?
end
end
class SubdomainBlank
def self.matches?(request)
request.subdomain.blank?
end
end
Rails.application.routes.draw do
constraints(SubdomainPresent) do
...
devise_for :users, controllers: {
omniauth_callbacks: 'omniauth_callbacks'
}
devise_scope :user do
get '/users/:id', to: 'users/registrations#show', as: "show_user"
end
...
end
end
My specific problem is that LinkedIn does not support wildcards with their callback URLs so I am lost on how I might be able to direct users to the right domain after OAuth authentication.

Answer 1

So it turns out the answer was to pass parameters in the authorization link which would eventually get passed to the callback action throught request.env["omniauth.params"]
Authorization Link format:
Here I was having trouble adding the parameters to the Devise URL builder so I just manually added the parameters. This can probably be moved to a url helper
<%= link_to "Connect your Linkedin", "#{omniauth_authorize_path(:user, :linkedin)}?subdomain=#{request.subdomain}" %>
Routes:
Then I defined a route constrained by a blank subdomain pointing to the callback action.
class SubdomainPresent
def self.matches?(request)
request.subdomain.present?
end
end
class SubdomainBlank
def self.matches?(request)
request.subdomain.blank?
end
end
Rails.application.routes.draw do
constraints(SubdomainPresent) do
...
devise_for :users, controllers: {
omniauth_callbacks: 'omniauth_callbacks'
}
resources :users
...
end
constraints(SubdomainBlank) do
root 'welcome#index'
...
devise_scope :user do
get 'linkedin/auth/callback', to: 'omniauth_callbacks#linkedin'
end
...
end
end
Controller:
I used this tutorial to set up my callback controllers: Rails 4 OmniAuth using Devise with Twitter, Facebook and Linkedin. My main objective with the callback controller was to have it reside in in the blank subdomain so I only had to give one call back URL to my LinkedIn Dev App. With this controller I search the omniauth params for the subdomain parameter and use that to switch to the proper schema.
def self.provides_callback_for(provider)
class_eval %Q{
def #{provider}
raise ArgumentError, "you need a subdomain parameter with this route" if request.env["omniauth.params"].empty?
subdomain = request.env["omniauth.params"]["subdomain"]
Apartment::Tenant.switch!(subdomain)
...
end
}
end

Answer 2

could you register each domain as a callback with linked (I guess if you have a lot that becomes unmanageable quickly).. You could cookie the user before sending them to linkedin so when they return you know which subdomain they belong to.