Grok filter extracting fields from message

Elastic Stack Logstash
8 
    dissect { mapping => { "message" => "%{ts} %{+ts} [%{thread}] %{loglevel} %{someField}{%{[@metadata][kvData]}}%{}" } }
    kv {
        source => "[@metadata][kvData]"
        field_split_pattern => ", "
    }

I changed the dissect to pull out the data between AuthenticationEvent{ and } into a separate field. That will result in

         "someField" => "c.c.d.c.s.a.UserAuthenticationListener - User logged in: AuthenticationEvent",
          "userName" => "username",
          "loglevel" => "INFO",
            "action" => "LOGIN",
         "userAgent" => "Chrome",
  "userAgentVersion" => "58.0.3029.110",
"productPermissions" => "bsg,rdm,dsm,catalog,helpdesk,policymanager,datadictionary,admin",
       "licenseType" => "CONSUMER",
     "failureReason" => "null",
           "timeout" => "1800000",
        "remoteHost" => "10.251.35.112",
         "timestamp" => "1592919002568",
         "sessionId" => "-303021888",
            "thread" => "https-jsse-nio-0.0.0.0-8443-exec-58",
                "ts" => "2020-06-23 15:30:02.568"