Add case_sensitive option for confirmation validation

Case :- 1. In case of email confirmation one needs case insensitive comparison
        2. In case of password confirmation one needs case sensitive comparison

[ci skip] Update Guides for case_sensitive option in confirmation validation

activemodel/CHANGELOG.md

@@ -58,4 +58,10 @@
 
     *Henrik Nyh*
 
+*   Add case_sensitive option for confirmation validator in models.
+
+    See #17351
+
+    *Akshat Sharma*
+
 Please check [4-1-stable](https://github.com/rails/rails/blob/4-1-stable/activemodel/CHANGELOG.md) for previous changes.

activemodel/lib/active_model/validations/confirmation.rb

@@ -3,14 +3,16 @@ module ActiveModel
   module Validations
     class ConfirmationValidator < EachValidator # :nodoc:
       def initialize(options)
-        super
+        super({ case_sensitive: true }.merge!(options))
         setup!(options[:class])
       end
 
       def validate_each(record, attribute, value)
-        if (confirmed = record.send("#{attribute}_confirmation")) && (value != confirmed)
-          human_attribute_name = record.class.human_attribute_name(attribute)
-          record.errors.add(:"#{attribute}_confirmation", :confirmation, options.merge(attribute: human_attribute_name))
+        if (confirmed = record.send("#{attribute}_confirmation"))
+          unless confimation_value_equal?(record, attribute, value, confirmed)
+            human_attribute_name = record.class.human_attribute_name(attribute)
+            record.errors.add(:"#{attribute}_confirmation", :confirmation, options.merge(attribute: human_attribute_name))
+          end
         end
       end
 
@@ -24,6 +26,14 @@ module ActiveModel
           :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation=")
         end.compact)
       end
+
+      def confimation_value_equal?(record, attribute, value, confirmed)
+        if !options[:case_sensitive] && value.is_a? String
+          value.casecmp(confirmed) == 0
+        else
+          value == confirmed
+        end
+      end
     end
 
     module HelperMethods
@@ -55,6 +65,8 @@ module ActiveModel
       # Configuration options:
       # * <tt>:message</tt> - A custom error message (default is: "doesn't match
       #   <tt>%{translated_attribute_name}</tt>").
+      # * <tt>:case_sensitive</tt> - Looks for an exact match. Ignored by
+      #   non-text columns (+true+ by default).
       #
       # There is also a list of default options supported by every validator:
       # +:if+, +:unless+, +:on+, +:allow_nil+, +:allow_blank+, and +:strict+.

guides/source/active_record_validations.md

@@ -327,6 +327,16 @@ class Person < ActiveRecord::Base
 end
 ```
 
+There is also a `:case_sensitive` option that you can use to define whether the
+confirmation constraint will be case sensitive or not. This option defaults to
+true.
+
+```ruby
+class Person < ActiveRecord::Base
+  validates :email, confirmation: { case_sensitive: false }
+end
+```
+
 The default error message for this helper is _"doesn't match confirmation"_.
 
 ### `exclusion`