Add load_available_adapters method

lib/rails_api_authentication.rb

@@ -24,6 +24,41 @@ module RailsApiAuthentication
     end
   end
 
+  # Private: Load the available adapters.
+  #
+  # adapters_short_names - Array of names of the adapters to load if available
+  #
+  # Example
+  #
+  #    load_available_adapters ['unavailable_adapter', 'available_adapter']
+  #    # => [RailsApiAuthentication::Adapters::AvailableAdapter]
+  #
+  # Returns an Array of available adapters
+  def self.load_available_adapters adapters_short_names
+    available_adapters = adapters_short_names.collect do |short_name|
+      next if short_name == 'rails' && (ActiveSupport.respond_to?(:version) && ActiveSupport.version >= Gem::Version.new('4.1.0'))
+      next if short_name == 'rails_api' && (ActiveSupport.respond_to?(:version) && ActiveSupport.version >= Gem::Version.new('5.0.0'))
+      adapter_name = "rails_api_authentication/adapters/#{short_name}_adapter"
+      if adapter_dependency_fulfilled?(short_name) && require(adapter_name)
+        adapter_name.camelize.constantize
+      end
+    end
+    available_adapters.compact!
+
+    available_adapters
+  end
+
+  def self.adapter_dependency_fulfilled? adapter_short_name
+    dependency = RailsApiAuthentication.adapters_dependencies[adapter_short_name]
+
+    if !respond_to?(:qualified_const_defined?) || (ActiveSupport.respond_to?(:version) && ActiveSupport.version.to_s =~ /^5\.0/)
+      # See https://github.com/gonzalo-bulnes/simple_token_authentication/pull/229/commits/74eda6c28cd0b45636c466de56f2dbaca5c5b629#r57507423
+      const_defined?(dependency)
+    else
+      qualified_const_defined?(dependency)
+    end
+  end
+
   available_model_adapters = load_available_adapters RailsApiAuthentication.model_adapters
   ensure_models_can_act_as_token_authenticatables available_model_adapters
 

lib/rails_api_authentication/configuration.rb

@@ -2,7 +2,9 @@ module RailsApiAuthentication
   module Configuration
     mattr_accessor :controller_adapters
     mattr_accessor :model_adapters
+    mattr_accessor :adapters_dependencies
 
+    @@controller_adapters = ['rails', 'rails_api', 'rails_metal']
     @@model_adapters = ['active_record', 'mongoid']
     @@adapters_dependencies = { 'active_record' => 'ActiveRecord::Base',
                                 'mongoid'       => 'Mongoid::Document',