nm-applet requires gnome-keyring (or any org.freedesktop.secrets provider) to ask for wlan password
Without gnome-keyring being installed I get no dialog to ask for a wifi password, but "Remote error from secret service: org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.secrets was not provided by any .service files".
Only when installing gnome-keyring (and the DBus service is provided), it asks me, logging "No keyring secrets found for SSID/802-11-wireless-security; asking user."
I think it should fall back to "asking user" also with org.freedesktop.secrets not being provided by any service files.
In the source this appears to be related to NM_SECRET_AGENT_GET_SECRETS_FLAG_ALLOW_INTERACTION, but maybe it does not even come there due to the previous DBus error?
I am using network-manager-applet 1.8.12-2 on Arch Linux.
I had gnome-keyring removed since a while already (2017-08). Not sure if any other services were providing org.freedesktop.secrets then until recently when this started to fail, or if I never had to provide a wlan password (at least I knew already that I could work around this by manually editing the connection).
The error comes from libsecret. Maybe keyring_find_secrets_cb is never called, or "g_cancellable_is_cancelled (r->cancellable)" there is true, i.e. it returns in the beginning already?
I assume that secret_service_search calls secret_service_get, which then throws the error.