TokenAuthenticatable allows non-unique tokens

Avoids needing an index to repeatedly check that
the token doesn't already exist when saving.

app/models/concerns/token_authenticatable.rb

@@ -10,6 +10,7 @@ module TokenAuthenticatable
 
     def add_authentication_token_field(token_field, options = {})
       @token_fields = [] unless @token_fields
+      unique = options.fetch(:unique, true)
 
       if @token_fields.include?(token_field)
         raise ArgumentError.new("#{token_field} already configured via add_authentication_token_field")
@@ -25,8 +26,10 @@ module TokenAuthenticatable
                    TokenAuthenticatableStrategies::Insecure.new(self, token_field, options)
                  end
 
-      define_singleton_method("find_by_#{token_field}") do |token|
-        strategy.find_token_authenticatable(token)
+      if unique
+        define_singleton_method("find_by_#{token_field}") do |token|
+          strategy.find_token_authenticatable(token)
+        end
       end
 
       define_method(token_field) do

app/models/concerns/token_authenticatable_strategies/base.rb

@@ -43,10 +43,14 @@ module TokenAuthenticatableStrategies
       set_token(instance, new_token)
     end
 
+    def unique
+      @options.fetch(:unique, true)
+    end
+
     def generate_available_token
       loop do
         token = generate_token
-        break token unless find_token_authenticatable(token, true)
+        break token unless unique && find_token_authenticatable(token, true)
       end
     end