wordpress: All Login Attempts Suddenly Fail With Error: Signature verification failed

This just started happening out of nowhere really. It was working fine until today. I haven’t made any changes or installed any updates since last week. All login attempts redirect to a page with this error:

There was a problem with your log in Error: There was an issue decoding the token, please review the Auth0 Plugin Error Log.

The logs in my Auth0 Dashboard show that the login was successful. There are no log messages from Auth0 plugin in my PHP logs or WP debug log. Please let me know what information you need that would help identify the problem. Thanks!

Edit:

Got this out of my wp database:

[
  {
    "section":"redirect_login\/decode",
    "code":"N\/A",
    "message":"Signature verification failed, disabling \"Settings \\ Basic \\ Client Secret Base64 Encoded\" may resolve this issue.",
    "date":1497967999
  },

cc: @glena @cocojoe