When methods that use POSTs are called on a acme.Client which has a nil Key field it will cause a deadlock due to an infinite loop in the code that looks up the account KID. This change adds a check for the key being nil, and errors out if that is the case. Also adds a test for this behavior. Fixes golang/go#38790 Change-Id: I65ff6bbbade7ed2d85306895904a976089730bbf Reviewed-on: https://go-review.googlesource.com/c/crypto/+/233164 Trust: Roland Shoemaker <roland@golang.org> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>