tumblr-auth.rb

require 'oauth'
require 'uri'

key = ''
secret = ''
consumer = OAuth::Consumer.new(key, secret, { site: 'http://www.tumblr.com' })
request_token = consumer.get_request_token(exclude_callback: true)

puts request_token.authorize_url
result = gets.chomp
uri = URI.parse(result)
verifier = Hash[uri.query.split('&').map { |el| el.split('=') }]['oauth_verifier']
oauth_token = request_token.get_access_token(oauth_verifier: query['oauth_verifier'])

puts oauth_token.token
puts oauth_token.secret