Omniauth: "Missing Template Error" - Ruby on Rails - ruby-on-rails

Question

I am building an API which authenticates via LinkedIn and then returns our tokens to the client.
The client will be written in AngularJS and will run separately.
Auth URL: http://example.com/users/auth/linkedin
I get the following error after authentication:
Missing template users/omniauth_callbacks/linkedin,
devise/omniauth_callbacks/linkedin, devise/linkedin,
application/linkedin with {
:locale=>[:en],
:formats=>[:html],
:variants=>[],
:handlers=>[:erb, :builder, :raw, :ruby, :coffee, :jbuilder]
}.
Searched in: * "/usr/local/lib/ruby/gems/2.2.0/gems/web-console-2.0.0/lib/action_dispatch/templates" * "/usr/local/Cellar/ruby/2.2.0/lib/ruby/gems/2.2.0/gems/devise-3.4.1/app/views"
I use the following special gems:
# Authentication
gem 'devise'
gem 'devise-token_authenticatable'
gem 'omniauth'
gem 'omniauth-oauth'
gem 'omniauth-linkedin'
# API Wrappers
gem 'linkedin'
The Source Code
config/routes.rb
# filename: routes.rb
# encoding: utf-8
Rails.application.routes.draw do
#
# API v1 Endpoints
#
scope '/api' do
## Authentication
devise_for :users,
:skip => [:sessions, :password, :registrations, :confirmation],
:controllers => {
:omniauth_callbacks => "users/omniauth_callbacks",
:registrations => "users/registrations",
:sessions => "users/sessions"
}
## User specific routes
scope '/users' do
devise_scope :user do
post '/check' => 'users/users#is_user', as: 'is_user'
post '/current' => 'users/sessions#get_current_user', as: 'current_user'
end
end
end
end
app/controllers/application_controller.rb
# filename: application_controller.rb
# encoding: utf-8
class ApplicationController < ActionController::Base
# Prevent CSRF attacks by raising an exception.
# For APIs, you may want to use :null_session instead.
protect_from_forgery with: :exception
before_filter :set_cors_headers
before_filter :cors_preflight
def set_cors_headers
headers['Access-Control-Allow-Origin'] = AppConfig.client['origin']
headers['Access-Control-Allow-Methods'] = 'GET,POST,PUT,DELETE,OPTIONS'
headers['Access-Control-Allow-Headers'] = '*'
headers['Access-Control-Max-Age'] = "3628800"
end
def cors_preflight
head(:ok) if request.method == :options
end
end
app/controllers/users/omniauth_callbacks_controller.rb
# filename: omniauth_callbacks_controller.rb
# encoding: utf-8
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
## Sign in / up with LinkedIn
def linkedin
auth_hash = request.env["omniauth.auth"]
auth = Authorization.find_by_provider_and_uid("linkedin", auth_hash['uid'])
if auth
## User already exists
user = auth.user
else
## User already signed in
unless current_user
unless user = User.find_by_email(auth_hash['info']['email'])
user = User.create({
first_name: auth_hash['info']['first_name'],
last_name: auth_hash['info']['last_name'],
email: auth_hash['info']['email'],
password: Devise.friendly_token[0,8]
})
end
## Sign user in
else
user = current_user
end
# Create an authorization for the current user
unless auth = user.authorizations.find_by_provider(auth_hash["provider"])
auth = user.authorizations.build(provider: auth_hash["provider"])
user.authorizations << auth
end
auth.update_attributes({
uid: auth_hash['uid'],
token: auth_hash['credentials']['token'],
secret: auth_hash['credentials']['secret'],
})
# Return user
user
end
end
end
app/controllers/users/registrations_controller.rb
# filename: registrations_controller.rb
# encoding: utf-8
class Users::RegistrationsController < Devise::RegistrationsControllerú
skip_before_filter :verify_authenticity_token
respond_to :json
def create
# Create the user
build_resource(sign_up_params)
# Try to save them
if resource.save
sign_in resource
render status: 200,
json: {
success: true,
info: "Registered",
data: {
user: resource,
auth_token: current_user.authentication_token
}
}
else
# Otherwise fail
render status: :unprocessable_entity,
json: {
success: false,
info: resource.errors,
data: {}
}
end
end
app/controllers/users/sessions_controller.rb
# filename: omniauth_callbacks_controller.rb
# encoding: utf-8
class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
## Sign in / up with LinkedIn
def linkedin
auth_hash = request.env["omniauth.auth"]
auth = Authorization.find_by_provider_and_uid("linkedin", auth_hash['uid'])
if auth
## User already exists
user = auth.user
else
## User already signed in
unless current_user
unless user = User.find_by_email(auth_hash['info']['email'])
user = User.create({
first_name: auth_hash['info']['first_name'],
last_name: auth_hash['info']['last_name'],
email: auth_hash['info']['email'],
password: Devise.friendly_token[0,8]
})
end
## Sign user in
else
user = current_user
end
# Create an authorization for the current user
unless auth = user.authorizations.find_by_provider(auth_hash["provider"])
auth = user.authorizations.build(provider: auth_hash["provider"])
user.authorizations << auth
end
auth.update_attributes({
uid: auth_hash['uid'],
token: auth_hash['credentials']['token'],
secret: auth_hash['credentials']['secret'],
})
# Return user
user
end
end
end
 app/controllers/users/users_controller.rb
# filename: users_controller.rb
# encoding: utf-8
class Users::UsersController < Devise::SessionsController
protect_from_forgery with: :exception, except: [:is_user]
respond_to :json
## Check if user exists by email
def is_user
#authenticate_user!
render status: 200, json: {
success: !User.find_by_email(params[:email]).blank?
}
end
end

Answer 1

Your linkedin method in the Users::OmniauthCallbacksController class doesn't render or redirect explicitly so it is attempting to do the implicit rendering of the linkedin template (usually linkedin.html.erb.
Based on your code you probably want to render user.to_json or something to that effect in your code so the angular api receives something it can work with.