It would appear that the authenticator could be called twice at almost exactly the same time by 2 or more clustered servers.

It would seem as if when there are 2 load balanced confluence servers with session affinity based on IP that it should not throw an error if you have a single request come in to login and that login involves calling an authenticator to check to see if a user exists and if not then creating it. However, we are getting unique constraint errors when this occurs.

This has been logged within support issue CSP-10474. Attached code used to replicate the issue. Latest info on that plugin at: https://spaces.internet2.edu/display/SHIB/ShibbolizedConfluence

It is also noted that this issue could be caused (with that code) because there are two requests on the same server at the same time to create the user. I'm going to contact them about this and implement a workaround to ignore unique constraint exceptions in this code, but we have only seen this occur when we were clustering more than one server, and it has occurred twice in the last week with a very small (<10 user) userbase.