emqx4.3/rel/config/examples/psk_authentication.conf.example

## Pre-Shared Keys authentication

psk_authentication {
    ## If init_file is specified, EMQX will import PSKs from the file into the built-in database at startup for use by the runtime
    init_file = "psk"

    ## The separator between PSKIdentity and SharedSecret in the PSK file
    separator = ":"

    ## The size of each chunk used to import to the built-in database from PSK file
    chunk_size = 50
 }