Overriding DeviseTokenAuth render_error()

override_devise_token_auth_render_error.rb

# Create a module, and put this somewhere your controllers can access.
# In this example, its assumed to be in the same dir as application_controller.rb
module DeviseTokenAuthRenderErrorOverride
  
  # 2. Overrides in application controller calling authenticate_user!
  # (or authenticate_[model]! if its a custom model)
  def render_authenticate_error
    render_error(401, I18n.t('devise.failure.unauthenticated'))
  end
  
  private
  
  # 1. Overrides in every DeviseTokenAuth controller
  # For example, the below method is called from
  #   DeviseTokenAuth::SessionsController
  #   DeviseTokenAuth::RegistrationsController
  #   ... etc
  # Here, you can serialize the response whatever way you want.
  # As a loose example, we are using our own MyErrorSerializer
  def render_error(status, message, data = nil)
    response = MyErrorSerializer.hash(status, message)
    response = response.merge(data) if data

    render status: status, json: response
  end

end

# In your ApplicationController prepend your override module such that
# the overrides you defined in the above module can apply to all child controllers
#
# Note that in this example, we are using ActionController::API since
# our application is assumed to be API-only
class ApplicationController < ActionController::API
  
  include DeviseTokenAuth::Concerns::SetUserByToken
  prepend DeviseTokenAuthRenderErrorOverride

  # remaining code...
end

# You will also need to create customer DeviseTokenAuth controllers for all the
# controllers in order to prepend the override module.
# Here is the official docs on how to do it:
# https://devise-token-auth.gitbook.io/devise-token-auth/usage/overrides#custom-controller-overrides
#
# Below is an example of one override controller
class Overrides::SessionsController < DeviseTokenAuth::SessionsController

  prepend DeviseTokenAuthRenderErrorOverride

end
# Do this for all the overwritable controllers