In extconfig.conf.sample from 20.8.1, you can read the following but I can’t find any res_config_curl.conf.sample file though a res_curl.conf.sample file exists.
; "odbc" is shown in the examples below, but is not the only valid realtime
; engine. Here are several of the possible options:
; odbc ... res_config_odbc
; sqlite3 ... res_config_sqlite3
; pgsql ... res_config_pgsql
; curl ... res_config_curl
Unlike other realtime backends, Asterisk does not have a specific configuration file for the realtime cURL backend. Instead, Asterisk gets the information it needs by reading the extconfig.conf file that it typically uses for general static and dynamic realtime configuration. The name of the realtime engine that Asterisk uses for cURL is called “curl” in extconfig.conf. Here is a sample: