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

@@ -5,15 +5,15 @@ module TokenAuthenticatable
   private
-  def write_new_token(token_field)
-    new_token = generate_available_token(token_field)
+  def write_new_token(token_field, unique: true)
+    new_token = generate_available_token(token_field, unique: unique)
     write_attribute(token_field, new_token)
   end
-  def generate_available_token(token_field)
+  def generate_available_token(token_field, unique:)
     loop do
       token = generate_token(token_field)
-      break token unless self.class.unscoped.find_by(token_field => token)
+      break token unless unique && self.class.unscoped.find_by(token_field => token)
     end
   end
@@ -28,17 +28,19 @@ module TokenAuthenticatable
     private # rubocop:disable Lint/UselessAccessModifier
-    def add_authentication_token_field(token_field)
+    def add_authentication_token_field(token_field, unique: true)
       @token_fields = [] unless @token_fields
       @token_fields << token_field
-      define_singleton_method("find_by_#{token_field}") do |token|
-        find_by(token_field => token) if token
+      if unique
+        define_singleton_method("find_by_#{token_field}") do |token|
+          find_by(token_field => token) if token
+        end
       end
       define_method("ensure_#{token_field}") do
         current_token = read_attribute(token_field)
-        current_token.blank? ? write_new_token(token_field) : current_token
+        current_token.blank? ? write_new_token(token_field, unique: unique) : current_token
       end
       define_method("set_#{token_field}") do |token|
@@ -54,7 +56,7 @@ module TokenAuthenticatable
       # Resets the token, but only saves when the database is in read & write mode
       define_method("reset_#{token_field}!") do
-        write_new_token(token_field)
+        write_new_token(token_field, unique: unique)
         save! if Gitlab::Database.read_write?
       end
     end