mastodon/db/seeds.rb

Doorkeeper::Application.create!(name: 'Web', superapp: true, redirect_uri: Doorkeeper.configuration.native_redirect_uri, scopes: 'read write follow')

if Rails.env.development?
  domain = ENV['LOCAL_DOMAIN'] || Rails.configuration.x.local_domain
  admin  = Account.where(username: 'admin').first_or_create!(username: 'admin')
  User.where(email: "admin@#{domain}").first_or_initialize(email: "admin@#{domain}", password: 'mastodonadmin', password_confirmation: 'mastodonadmin', confirmed_at: Time.now.utc, admin: true, account: admin).save!
end