Hi @fxposter,
There isn't an ACME endpoint to retrieve a total list of pending authorizations for an account, and Boulder/LE don't provide one above-and-beyond what ACME specifies. There also isn't a user-visible metric for how many pending authorizations have accrued, though that may be something we could think about.
You can request a rate limit adjustment for this limit. Please be sure to include all of the requested information - folks frequently miss something and based on the volume of requests & our staff size we often can't follow-up if the request is incomplete.
How frequently do you rebase against the latest code from Lego master? In particular I know this commit has supposedly helped with some pending authorization leaks experienced by this client. Does your fork include that commit?
In general it should be possible to carefully log all of the authorizations created to do the bookkeeping required to count pending authorizations and to know whether any have been leaked. If you're regularly leaking authorizations using Lego I would encourage you to try and work with the Lego upstream to resolve the root cause since it is indicative of a client bug or a corner case.
Hope this helps!