You've stay in a cafe?

You have private mobile router or tethering with enough data transfer rate? No?

You've tried to connect free hotspot Wi-Fi?(Tully's, Starbucks, and so on.)

You've opened a browser?

Frequently you can't seen Wi-Fi login page?

When I have this issue, I'll find login page manually following way.

Find the following IP address

1. Find Default gateway
2. Find DNS server(Fully recursive)

Enter each address in to browser that you've got.

You may be shows Wi-Fi authentication page.

Default gateway also have same IP address of DNS server.

Following commands.

lasthope-mbp:~ wnoguchi$ route get 0.0.0.0
   route to: default
destination: default
       mask: default
    gateway: 10.0.0.1
  interface: en0
      flags: <UP,GATEWAY,DONE,STATIC,PRCLONING>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0         0         0         0         0      1500         0
lasthope-mbp:~ wnoguchi$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 56 data bytes
^C
--- 8.8.8.8 ping statistics ---
1 packets transmitted, 0 packets received, 100.0% packet loss
lasthope-mbp:~ wnoguchi$ ping 10.0.0.1
PING 10.0.0.1 (10.0.0.1): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
Request timeout for icmp_seq 2
^C
--- 10.0.0.1 ping statistics ---
4 packets transmitted, 0 packets received, 100.0% packet loss
lasthope-mbp:~ wnoguchi$ dig www.google.com

; <<>> DiG 9.10.6 <<>> www.google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27522
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1400
;; QUESTION SECTION:
;www.google.com.			IN	A

;; ANSWER SECTION:
www.google.com.		37	IN	A	172.217.161.228

;; Query time: 32 msec
;; SERVER: 198.51.100.123#53(198.51.100.123)
;; WHEN: Wed Dec 19 10:59:47 JST 2018
;; MSG SIZE  rcvd: 59

In this example, following results are possible login page address.

    gateway: 10.0.0.1

;; SERVER: 198.51.100.123#53(198.51.100.123)

Have fun, internet junkie.