Custom failure app to render a custom json on auth failure

custom_auth_failure_app.rb

class CustomAuthFailure < Devise::FailureApp
  def respond
    self.status = 401 
    self.content_type = 'json'
    self.response_body = {"errors" => ["Invalid login credentials"]}.to_json
  end 
end

And tell devise to use the custom failure app by adding the following to config/initializers/devise.rb :

  config.warden do |manager|
    manager.failure_app = CustomAuthFailure
  end 

thx very good

Alternative approach which I opted for after seeing this and reading Devise::FailureApp was to override the http_auth_body method instead of the respond method. I also used the inbuilt i18n_message method to populate the error field.

class FailureApp < Devise::FailureApp
  def http_auth_body
      {
          errors: [
              {
                  id: :unauthorized,
                  status: 401,
                  title: i18n_message
              }
          ]
      }.to_json
  end
end

The reason I wanted to customize the failure handling in the first place was to make the error messages comply with the JSON API standard. so that is what you are seeing here.

Or see https://stackoverflow.com/questions/7297183/custom-devise-401-unauthorized-response/35299936#35299936 for a failure app that handles json and fall back to normal use otherwise

I've used this implementation and it works almost every time. The problem appears when I try to register a user with an existing email address. Rails will skip right to a PG exception. Any thoughts?

I've used this implementation and it works almost every time. The problem appears when I try to register a user with an existing email address. Rails will skip right to a PG exception. Any thoughts?

You're getting the PG exception probably because you're missing the validations on the User model.