users: require email verification for signups from proxies.

Require users who signup using proxies to verify their email addresses
before they can perform any edits. For verification purposes, the email
must be a nondisposable address from a whitelist of trusted email
providers.

app/models/email_address.rb

@@ -2,24 +2,33 @@ class EmailAddress < ApplicationRecord
   # https://www.regular-expressions.info/email.html
   EMAIL_REGEX = /\A[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}\z/
 
-  belongs_to :user
+  belongs_to :user, inverse_of: :email_address
 
   validates :address, presence: true, confirmation: true, format: { with: EMAIL_REGEX }
   validates :normalized_address, uniqueness: true
   validates :user_id, uniqueness: true
   validate :validate_deliverable, on: :deliverable
+  after_save :update_user
 
   def address=(value)
     self.normalized_address = EmailValidator.normalize(value) || address
     super
   end
 
+  def nondisposable?
+    EmailValidator.nondisposable?(address)
+  end
+
   def validate_deliverable
     if EmailValidator.undeliverable?(address)
       errors[:address] << "is invalid or does not exist"
     end
   end
 
+  def update_user
+    user.update!(is_verified: is_verified? && nondisposable?)
+  end
+
   concerning :VerificationMethods do
     def verifier
       @verifier ||= Danbooru::MessageVerifier.new(:email_verification_key)

app/models/user.rb

@@ -63,6 +63,8 @@ class User < ApplicationRecord
     opt_out_tracking
     no_flagging
     no_feedback
+    requires_verification
+    is_verified
   )
 
   has_bit_flags BOOLEAN_ATTRIBUTES, :field => "bit_prefs"