Add canonical e-mail blocks for suspended accounts (#16049)

Prevent new accounts from being created using the same underlying
e-mail as a suspended account using extensions and period
permutations. Stores e-mails as a SHA256 hash

app/validators/blacklisted_email_validator.rb

@@ -6,26 +6,25 @@ class BlacklistedEmailValidator < ActiveModel::Validator
 
     @email = user.email
 
-    user.errors.add(:email, :blocked) if blocked_email?
+    user.errors.add(:email, :blocked) if blocked_email_provider?
+    user.errors.add(:email, :taken) if blocked_canonical_email?
   end
 
   private
 
-  def blocked_email?
-    on_blacklist? || not_on_whitelist?
+  def blocked_email_provider?
+    disallowed_through_email_domain_block? || disallowed_through_configuration? || not_allowed_through_configuration?
   end
 
-  def on_blacklist?
-    return true  if EmailDomainBlock.block?(@email)
-    return false if Rails.configuration.x.email_domains_blacklist.blank?
-
-    domains = Rails.configuration.x.email_domains_blacklist.gsub('.', '\.')
-    regexp  = Regexp.new("@(.+\\.)?(#{domains})", true)
-
-    regexp.match?(@email)
+  def blocked_canonical_email?
+    CanonicalEmailBlock.block?(@email)
   end
 
-  def not_on_whitelist?
+  def disallowed_through_email_domain_block?
+    EmailDomainBlock.block?(@email)
+  end
+
+  def not_allowed_through_configuration?
     return false if Rails.configuration.x.email_domains_whitelist.blank?
 
     domains = Rails.configuration.x.email_domains_whitelist.gsub('.', '\.')
@@ -33,4 +32,13 @@ class BlacklistedEmailValidator < ActiveModel::Validator
 
     @email !~ regexp
   end
+
+  def disallowed_through_configuration?
+    return false if Rails.configuration.x.email_domains_blacklist.blank?
+
+    domains = Rails.configuration.x.email_domains_blacklist.gsub('.', '\.')
+    regexp  = Regexp.new("@(.+\\.)?(#{domains})", true)
+
+    regexp.match?(@email)
+  end
 end