A certificate validation operation took xxxx milliseconds and has exceeded the execution time threshold
I have just noticed the following message logged several times in the Application Event Log on a SharePoint 2013 Application server:
A certificate validation operation took 23369.387 milliseconds and has exceeded the execution time threshold. If this continues to occur, it may represent a configuration issue. Please see http://go.microsoft.com/fwlink/?LinkId=246987 for more details.
I found the solution to this in Microsoft KB2625048 (not the link included in the error message). I used Workaround 1 to install the SharePoint Root Authority certificate in the Trusted Root Certification Authorities store.