twitter_application_bearer_token.rb

consumer_key_secret = "#{Settings.twitter_key}:#{Settings.twitter_secret}"
encoded_key_secret  = Base64.strict_encode64(consumer_key_secret)

headers = {
  'Authorization' => "Basic #{encoded_key_secret}",
  'Content-Type'  => "application/x-www-form-urlencoded;charset=UTF-8"
}

body = 'grant_type=client_credentials'

begin
  response = HTTParty.post('https://api.twitter.com/oauth2/token', body: body, headers: headers)
rescue Exception => e
  return { code: 403, response: e.message }
end

if response.code == 200
  response['access_token']
end