credentials vs laissez-passer

credentials

noun
  • Documentary evidence of someone's right to credit or authority, especially such a document given to an ambassador by a country. 

  • login data 

laissez-passer

noun
  • A pass or permit; a document permitting the bearer to travel, sometimes issued as an emergency passport. 

How often have the words credentials and laissez-passer occurred in a corpus of books? (source: Google Ngram Viewer )