SHA1 certificates for secure SSL/TLS communications are deprecated due to known computational vulnerabilities. To ensure secure communications, a forced deprecation sounds reasonable (i.e. refuse to connect to these). That has the side effect that it will lock out many users who are unable to use stronger hashes such as SHA256. However, if a fallback to SHA1 is provided (as Facebook is proposing), everyone will be vulnerable to SHA1 downgrade man-in-the-middle attacks.
What to do?
(Score: 3, Informative) by frojack on Friday December 11 2015, @08:03PM
Facebook already has a work-around [facebook.com] to force downgrade to http from their https-by-default policy.
(I find it odd that facebook, which is all about duping everyone into releasing every private detail of their lives to the world is even bothering with https).
No, you are mistaken. I've always had this sig.