Implement access token to ease credential downloading.

Allow to query the web site without copy/pasting the user SSL certificates.
The query should be like:
curl -X POST -H "X-Access-Token: ACCESSTOKENVALUE" "https://slaposmaster.example.org/myspace/my_account/request-a-certificate/WebSection_requestNewCertificate"

Access token is destroyed after usage.
The token validity is one day.