Add username to ASA Security negotiation log

CHANGELOG.next.asciidoc

@@ -310,6 +310,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - sophos/xg fileset: Add missing pipeline for System Health logs. {pull}27827[27827] {issue}27826[27826]
 - Resolve issue with @timestamp for defender_atp. {pull}28272[28272]
 - Tolerate faults when Windows Event Log session is interrupted {issue}27947[27947] {pull}28191[28191]
+- Add support for username in cisco asa security negotiation logs {pull}26975[26975]
 
 *Heartbeat*
 

x-pack/filebeat/module/cisco/asa/test/additional_messages.log

@@ -91,3 +91,4 @@ May  5 19:02:25 dev01: %ASA-4-733100: [ Scanning] drop rate-2 exceeded. Current
 May  5 19:02:25 dev01: %ASA-4-733100: [   192.168.0.1] drop rate-1 exceeded. Current burst rate is 0 per second, max configured rate is 10; Current average rate is 5 per second, max configured rate is 5; Cumulative total count is 6018
 May  5 19:02:25 dev01: %ASA-4-733100: [     Port-5432 5432] drop rate-1 exceeded. Current burst rate is 8 per second, max configured rate is 10; Current average rate is 20 per second, max configured rate is 5; Cumulative total count is 12466
 May  5 19:02:25 dev01: %ASA-4-733100: [           RDP 3389] drop rate-1 exceeded. Current burst rate is 63 per second, max configured rate is 10; Current average rate is 5 per second, max configured rate is 5; Cumulative total count is 3054
+Apr 27 2020 02:03:03 dev01: %ASA-6-713901: Group = 100.60.140.10, Username = test_user, IP = 1.2.3.4, Security negotiation complete for User (test_user) Responder, Inbound SPI = 0x0000000, Outbound SPI = 0x0000000