title: When Service Account should be used to access google api?
body: <p>I am trying to use google api for getting new emails from gmail account. However reading the docs I found that there are two types to access api the first one without authorization (with json credential) and second one one is Service Account (with p12 certificate and secretkey)</p>
  
  <p>Can not understand what the difference between this access? What exactly should I use?</p>
  
  <p>Thanks</p>