Facebook is updating its encryption requirements for Facebook-connected apps which means that apps that don't support SHA-2 certificate signatures will no longer be able to connect to Facebook starting on October 1, 2015.
Facebook’s Adam Gross in a recent post on the Facebook developer blog:
These changes are part of a broader shift in how browsers and web sites encrypt traffic to protect the contents of online communications. Typically, web browsers use a hash function to create a unique fingerprint for a chunk of data or a message. This fingerprint is then digitally signed to prove that a message has not been altered or tampered with when passing through the various servers and systems between your computer and Facebook's servers.
For the past two decades, the SHA-1 standard has been the preferred choice across the Internet for calculating message fingerprints. But after identifying security weaknesses in SHA-1, the Certificate Authority and Browser Forum recently published new Baseline Requirements for SSL recommending that all certificate authorities transition away from SHA-1 based signatures, with a full sunset date of January 1, 2016.
We'll be updating our servers to stop accepting SHA-1 based connections before this final date, on October 1, 2015. After that date, we'll require apps and sites that connect to Facebook to support the more secure SHA-2 connections.
We recommend that developers check their applications, SDKs, or devices that connect to Facebook to ensure they support the SHA-2 standard. If your app already supports this standard, then no action is necessary. But if your app relies on SHA-1 based certificate verification, then people may encounter broken experiences in your app if you fail to update it.