Looks like the port 5240 is from /MAAS/api/2.0/describe/.


$ curl -s http://192.168.12.19:80/MAAS/api/2.0/describe/ | jq -r .handlers[].uri | head
http://192.168.12.19:5240/MAAS/api/2.0/nodes/
http://192.168.12.19:5240/MAAS/api/2.0/files/
http://192.168.12.19:5240/MAAS/api/2.0/machines/
http://192.168.12.19:5240/MAAS/api/2.0/nodes/
http://192.168.12.19:5240/MAAS/api/2.0/nodes/
http://192.168.12.19:5240/MAAS/api/2.0/nodes/
http://192.168.12.19:5240/MAAS/api/2.0/version/
http://192.168.12.19:5240/MAAS/api/2.0/account/
http://192.168.12.19:5240/MAAS/api/2.0/nodes/{system_id}/bcache-cache-set/{id}/
http://192.168.12.19:5240/MAAS/api/2.0/nodes/{system_id}/bcache-cache-sets/


$ strace -e network maas login admin http://192.168.12.19:80/MAAS/api/2.0/ gqG3GBeepxPaaHcRPQ:ZAtMA4XXJ4WnqkNTG9:MnczDFaPSs4tKZnV8zWLBnd3SKwNa79v
socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_IP) = 3
bind(3, {sa_family=AF_INET6, sin6_port=htons(0), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_scope_id=0}, 28) = 0
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=137639, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_TCP) = 3
setsockopt(3, SOL_TCP, TCP_NODELAY, [1], 4) = 0
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("192.168.12.19")}, 16) = 0
sendto(3, "GET /MAAS/api/2.0/users/?op=whoa"..., 426, 0, NULL, 0) = 426
recvfrom(3, "HTTP/1.1 200 OK\r\nServer: nginx/1"..., 8192, 0, NULL, NULL) = 468
getsockname(3, {sa_family=AF_INET, sin_port=htons(60546), sin_addr=inet_addr("10.0.8.190")}, [16]) = 0
getpeername(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("192.168.12.19")}, [16]) = 0
socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC, IPPROTO_TCP) = 3
setsockopt(3, SOL_TCP, TCP_NODELAY, [1], 4) = 0
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("192.168.12.19")}, 16) = 0
sendto(3, "GET /MAAS/api/2.0/describe/ HTTP"..., 136, 0, NULL, 0) = 136
recvfrom(3, "HTTP/1.1 200 OK\r\nServer: nginx/1"..., 8192, 0, NULL, NULL) = 8192
recvfrom(3, " String\\n\\n \", \"method\": \"POST\","..., 516096, 0, NULL, NULL) = 5801
recvfrom(3, ", \"name\": \"delete\", \"op\": null, "..., 507904, 0, NULL, NULL) = 28960
recvfrom(3, "am not_fabrics: Optional.  Only "..., 483328, 0, NULL, NULL) = 10136
recvfrom(3, "et_serial\", \"restful\": false}], "..., 466944, 0, NULL, NULL) = 27112
recvfrom(3, "nterfacesHandler\", \"params\": [\"s"..., 442368, 0, NULL, NULL) = 7240
recvfrom(3, "privilege level.         The def"..., 434176, 0, NULL, NULL) = 55424
recvfrom(3, "t (and when the enlistment is do"..., 376832, 0, NULL, NULL) = 14480
recvfrom(3, "n\", \"method\": \"GET\", \"name\": \"de"..., 368640, 0, NULL, NULL) = 17376
recvfrom(3, "endor_name``: The device vendor "..., 352256, 0, NULL, NULL) = 40544
recvfrom(3, "ubnets: Optional.  Only nodes wi"..., 311296, 0, NULL, NULL) = 26064
recvfrom(3, "e VLAN\\n\\nRetrieves a VLAN on a "..., 278528, 0, NULL, NULL) = 43440
recvfrom(3, "oolean\\n\\n :param node: Optional"..., 237568, 0, NULL, NULL) = 125976
recvfrom(3, "ne or more devices containing th"..., 114688, 0, NULL, NULL) = 30408
recvfrom(3, " user.\\n\\nNotifications that hav"..., 81920, 0, NULL, NULL) = 40544
recvfrom(3, "}, \"name\": \"RegionControllersHan"..., 40960, 0, NULL, NULL) = 30408
recvfrom(3, "l.  The architecture of\\nthe new"..., 8192, 0, NULL, NULL) = 8192
recvfrom(3, "\\n\\n :param add_partitions: Opti"..., 8192, 0, NULL, NULL) = 7222
getsockname(3, {sa_family=AF_INET, sin_port=htons(60562), sin_addr=inet_addr("10.0.8.190")}, [16]) = 0
getpeername(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("192.168.12.19")}, [16]) = 0

You are now logged in to the MAAS server at
http://192.168.12.19:80/MAAS/api/2.0/ with the profile name 'admin'.

For help with the available commands, try:

  maas admin --help

+++ exited with 0 +++