Thanks for the answers, Jens.
The problem I have is the iOS app is only able to do push replication, pull replication doesn’t happen at all. I asked this CredStore thing because I thought this was the cause (as this CredStore error always shows up before I should see some result of pull replication printed to the Xcode console.). I found that stackoverflow thread too, I followed the suggestion in the best answer, but did not solve the problem.
If you are sure CredStore is not the cause of pull replication problem, could you give some suggestion on how to debug this problem? CBL of my iOS app is set up following the Couchbase Connect 2017’s Couchbase Mobile tutorial (the link to it that used to work: https://github.com/couchbaselabs/mobile-training-todo/blob/master/ios/Todo). view/livequery and push/pull replications are all identical to the example code given, nothing added/subtracted/modified.
FYI, when the app make GET and POST requests to other servers, everything works fine and no CredStore error showed up.
Regarding version of CBL, the iOS app started off with 1.4.1, encountered this pull replication problem accompanied by this CredStore error, thinking maybe 1.4.1 is doing something fancy behind the scene during pull replication, so I downgraded to CBL1.3.1, which is the version I used for Android version of this app (never had any replication problem, by the way), only to find out 1.3.1 has the identical problem accompanied by the identical error… Anyway, the plan is to stick to CBL 1.3.1 for current release of the app (as there’s no time and appetite to learn how things work in later versions and re-write the code), but will surely try CBL 2.x in next release.