Question: Mac OS Safari and Windows Authentication

[boris-meerovich-sp]

GoBetween: 0.7.0 runs on Windows 2012 R2
The LB manages 2 Windows 2012 R2 servers with IIS configured as 'Windows Authentication'.
All browsers on Windows runs as expected with succeed Kerberos login.
On Mac OS Catalina 10.15.2 Google Chrome also makes the authentication successfully.
Although, Safari 13.0.4 and Firefox don't pass the authentication step.
Browser authentication window with user and password are displayed even correct credentials are set.
When I go to the server directly, authentication passed succeed.

Is there something I missed with the configuration?
Please, advice.

config file:
[servers.sample]
bind = "server:80"
protocol = "tcp" 
balance = "roundrobin"

max_connections = 10000
client_idle_timeout = "10m"
backend_idle_timeout = "10m"
backend_connection_timeout = "2s"

    [servers.sample.discovery]
    kind = "static"
    static_list = [           
      "172.17.40.45:80 weight=1",
	  "172.17.40.35:80 weight=1"  
    ]

    [servers.sample.healthcheck]
    fails = 1                      
    passes = 1
    interval = "2s"   
    timeout="1s"             
    kind = "ping"
    ping_timeout_duration = "500ms"
	
	[logging]
level = "debug"   # "debug" | "info" | "warn" | "error"
output = "stdout" # "stdout" | "stderr" | "/path/to/gobetween.log"